Base building sim games are an odd genre. The majority of the gameplay involves managing a base, placing buildings, managing schedules, optimizing proximity, rationing resources, and in general doing a lot of what, anywhere else, would be considered work. Fortunately, a lot of what actually looks like work is what the appeal of these games are. Base building sim games allow you to experience the feeling of dealing with a certain setting, often based in fantasy or science fiction. You can build a thriving town or kingdom. You can manage a small group of settlers as they attempt to survive, and thrive, in a wild new land. You can manage a number of clones as they find themselves stranded deep inside an asteroid.
Base building sim games represent these possibilities and many more. There is a large amount of variation within the genre, but let’s focus on one specific game as we explore what actually makes this genre interesting to play and explore.
Oxygen Not Included is, as far as I know, one-of-a-kind. There is nothing else like it, and so far as I can tell, there won’t be much quite like it for quite a while to come. Oxygen Not Included (or ONI, a delightful acronym commonly used for the game) is a colony-management-basebuilding sim in a similar vein to Rimworld or Dwarf Fortress, but with an extreme emphasis on the manipulation of systems.
While the game itself is technically focused on your work as an AI trying to determine what has happened to you and your ‘dupes’ (duplicates, or some sort of.. clones) after you spontaneously appear in the center of an asteroid, in reality, ONI takes a very backseat approach to story-telling. One must go out of their way to find the story, and the game is truly alive only when problem solving. This is relatively common among all base building sim games, though there are exceptions.
The actual gameplay surrounds the development of a colony within the asteroid you and your dupes have arrived at. Your first few cycles (or even entire attempts!) will likely be focused almost entirely upon learning the most basic aspects of the game. For example, one of your first priorities is to find water. A second, to produce oxygen. A third, to make sure your dupes have a bathroom so that they won’t make a mess, leaving polluted water all over your base and making any dupes who walk in it grimace with disgust. It seems slightly ironic that I’ve found so much fun in a game that requires teaching your cloned humanoid things what they should build so that they don’t pee themselves.
After you’ve set everything up, dupes will take care of themselves. They’ll manage their own duties, following a prioritization system, and follow a schedule you create (or you can use the default schedule). You can make specific buildings that allow dupes to build things, such as oxygen masks or produce food. Dupes can farm, cultivate, or work with animals, grooming or watching over creature eggs. There are numerous different buildings to be built, all of which provide some benefit, and even make it simpler to do some of the more complex things that can be done in the game.
This is one of the core appeals of a base building sim game - building. New buildings provide several benefits. First of all, it provides a sense of progression. This is an important aspect of all games, where the sense of progression can be one of the most important factors. Next, new buildings will generally enable you to do something new. This can be recruit more people - though in ONI you aren’t limited by how many you can recruit, but by how many you can support - or build something new. In ONI, buildings generally support some other part of your base, like batteries hold electricity to keep your base running long term, or allow you to produce something. The metal refinery, for example, allows you to refine metal. This is an important milestone in ONI because refined metal allows you to create significantly more complex buildings, which allow you to add increasingly complex aspects to your base.
With the buildings alone, though, the game would be - perhaps not uninteresting, but certainly nothing especially notable. Add in the more complex systems, though, and we rapidly approach a masterpiece in game design – at least, from the perspective of the creative problem solver. ONI has a fluid system that emulates the propagation of fluids and gas throughout an area. Entire sections of your base can be taken up, if you wish, in only storing water. As the name so aptly notes, oxygen is not freely included. You will have to find more or make more, and provide it to your dupes. Many places across the asteroid do not have oxygen, or some places have polluted oxygen, or even oxygen infected with germs. It is entirely possible to have a large base well into the mid-game fall apart due to issues with oxygen production. Alas.
The fluid system even has a density simulation, which causes denser gases or fluids to fall to the bottom, while less dense matter rises. Eventually, everyone will have a moment of panic as they realize the entire top portion of their base is entirely made up of hydrogen, and now dupes are unable to sleep because their bedrooms have no oxygen to breathe.
The base building mechanics play into these simulation mechanics quite deeply. There are a couple of buildings which are directly meant to create more oxygen to supply your base. To illustrate the depth of the simulation, your duplicants not only inhale oxygen, but they exhale carbon dioxide. This can be a problem, because you will eventually need to get rid of that so your base won’t become oversaturated with a gas that isn’t oxygen. Thankfully, carbon dioxide is heavier than oxygen, so it will slowly fall to the bottom of your base. This means you can place a carbon skimmer - a building which lets you remove carbon dioxide from the air - to remove it all from your base.
Another system, one of the humblest, though definitely the most consequential, is that of temperature. Objects touching will transfer energy according to how fast heat energy propagates between them, and how much energy can be absorbed by a material.
This mechanic leads to some of the most interesting methods of solving a problem that I’ve ever experienced. For example, one of the hurdles to jumping from the early game to the mid game, and even getting into the late game, is temperature management. If you have too many power generators in your base, your base will get too hot. This can make it so that your food crops won’t grow anymore, leading your dupes to starve. Some objects may overheat, making them unusable, requiring repairs. Even something as mundane as the water piped into an electrolyzer, a building meant to split water into hydrogen and oxygen, can cause your base to heat up because the lowest temperature that the resulting oxygen will appear at is 30 C (86 F), a number barely low enough to allow farming some of the easiest staples of the duplicant diet.
Temperature management is not limited to prevention, though. There are multiple cases where large amounts of heat can be taken and used for their benefits. One example is the clear-cut steam engine, which allows using excessive heat to run a steam engine by boiling water. This can be coupled with a thermo aqua-tuner which allows, in simplest terms, transporting heat from elsewhere on the asteroid (or your base!) and depositing it into the area around the thermal aqua-tuner. If you happen to have water sitting on the aqua-tuner, you can easily boil the water into steam, providing energy for the steam engine.
In a significantly more complex example, crude oil can be cracked solely using extreme amounts of heat in order to create petroleum, rather than using a building dedicated to this purpose. If petroleum is boiled, this will create sour gas, which can be cooled to create methane. If reheated, this becomes natural gas, another resource which can be used for powering your base. Why not use the building, you may ask? Because it’s less efficient to use the building rather than to set up a system which directly heats the oil and keeps all of the ensuing product.
Managing temperature even goes so far as to demand, before finishing the game, that you learn how to manipulate temperature to such a degree that you can create liquid hydrogen and liquid oxygen as fuel and oxidizer for rockets. These feats cannot be accomplished directly with a building - you must master the problem solving techniques of ONI before you can manage this and complete everything the game has to offer.
All of this provides a robust system in which players can problem solve in just about any way they like. Imagine you have a vent (an infinite source of some resource, which expels said resource periodically) which releases gas at a temperature too high for the buildings used to process it. One option is to seal up the area and provide some metal tiles which can conduct the heat out of the room and into another, where you may have a large amount of water and a steam engine, ready to soak up the extra heat and even put it to use!
These systems don’t even take up the entirety of the game. Once you’ve made a functioning base, your work in ONI has only just begun. ONI also boasts an interesting space exploration system, and while more detailed and fun (in my opinion) in the expansion Spaced Out!, even the vanilla space exploration experience is quite interesting. You’ll need to dig your way up to the surface of your asteroid in order to begin exploring space - but space is another frontier you’ll need to conquer.
One point of note about ONI is that there are multiple different biomes found on the asteroids that you’ll be inhabiting. Take the ice biome - where everything is covered in ice, plants suck the heat straight out of the air around them, and slush sits waiting to drip into your base. The oil biome, near the bottom edges of the asteroid, are where you’ll find the majority of your oil. Swamp biomes host plenty of polluted water and a number of animals that thrive in the disgusting conditions.
Space is just another biome like these - except (at least in the original version of the vanilla game) it actively worked against you. Meteors would crash down onto the surface periodically, requiring you to either manually clear the debris, or set up an automated system. If you didn’t, you would be unable to manage any sort of base on the surface. Why? Because the meteors would, naturally, crash into and destroy all of your buildings. Coupled with the intense light and heat of the sun far above, and even spending too much time on the surface of the asteroid could damage your dupes.
All of this comes together to create an experience where you have to juggle building your base and managing its development with sustainability. It showcases many of the most interesting aspects of base building sim games with its mechanics. ONI manages to make managing a number of AI controlled units one of the more interesting mechanics in the game - duplicants must have places to sleep, food to eat, oxygen to breathe, and as you progress into the game, they will also need to have better morale to support their growing duties. As you get even farther into the game, you’ll have to figure out how to optimize their ability to run to their duties, because otherwise it could take them too long to ever get around to doing something.
Between this, the different buildings, and the systemic mechanics, ONI provides quite a few number of interesting challenges to solve - and this is what makes it an enjoyable game. The problems it tasks you with solving aren’t even necessarily set out explicitly, but rather something you arrive at organically. This is a fundamental design that is common in almost every well-received base building sim game - emergent challenges. These are challenges which you’ll likely need to overcome, but aren’t explicitly set, rather one that happens as a result of the game itself. These are some of the most interesting challenges to overcome, and are part of the reason why base building sim games are fun.
Emergent gameplay, gameplay that arises as a direct result of interconnecting systems, is a powerful way to create a game that is fun to play over and over. This is why certain base builder sim games like Rimworld or Dwarf Fortress are so popular. While those games focus more allowing the emergent gameplay to create interesting storytelling - a story you devise as you play, reacting to every random happenstance - ONI focuses on creating interesting challenges.
There are not many games where you might eventually find yourself pondering how to ‘tame’ a volcano to harvest its molten gold by transferring its heat to a steam engine to harvest the additional heat for power while cooling down the gold so that it becomes usable. While this scenario is unique to ONI, the sort of problem solving that is not given as a ‘mission’ by the game, but rather an objective that can optionally be set by the player, is a fantastic way to make the game interesting over a long period of time. This creative problem solving also plays into the sense of progression mentioned earlier. Many of these problems allow the player to gain something that helps their base, their units, or whatever the game is about, to expand their capabilities. Voila, progression.
Exploration also plays a part in making these games interesting. Many of these games come with only a minor set of guidelines, with little if any tutorial. This makes exploration of the mechanics something the player must complete on their own. Unfortunately, this can mean that these games can be somewhat harder to approach than others, but it does mean that learning how to play the game is full of interesting decisions and surprises. ONI, for example, will likely have many scenarios where you need to figure out what is going wrong in your base. Why are duplicants taking so long to get something done? Why are they getting sick, or having nervous breakdowns? Why did they pee themselves? Why did that one just suddenly trap himself? How did that one just suddenly die? These, and many more, are common problems even to players that have played the game for hundreds of hours. Learning how to play the game, discovering the way it works, setting objectives, and solving the problems presented by the mechanics are a natural progression of playing the game, and it is one of the reasons these games are so interesting.
This progression is not solely for beginners, though. Setting objectives and solving problems is a recurring aspect of the game, which is enabled by the emergent mechanics. Because there is so much freedom in how you can interact with the game, there are numerous ways to do things. This gives replayability, and the option to create more challenging conditions for yourself on repeat playthroughs. Let’s use oxygen production as an example. For a while, you can use an Oxygen Diffuser, which will convert algae into oxygen. The problem is that your algae is likely limited, and the amount of oxygen produced by a diffuser is not all that high. Alternatively, you can use an electrolyzer. This lets you split water into hydrogen and oxygen. Eventually, though, you might notice a couple problems.
The first is that the oxygen coming out of an electrolyzer is relatively warm, which can mean issues for your food production. You’ll have to figure out how to cool it, or to at least cool your crops. Second, what do you do with all of the hydrogen that you’ve been making? There are numerous ways to handle the heating, including routing it through a cooler biome, creating a cooling loop, or even an Anti Entropy Thermo-Nullifier (AETN), which will cool the area around it if you pipe in hydrogen. If you don’t have an AETN, then you’ll have to figure out a different use for that hydrogen. Thankfully, there’s a hydrogen generator, which means you can generate power with all of that excess hydrogen. In fact, the hydrogen generator actually produces enough power that you can make an entirely self-sufficient (in terms of power) system to continually create oxygen for yourself.
Base building sim games are a small genre, but many of them have a huge amount of replayability. Games like ONI, Rimworld, Dwarf Fortress, and other base builders which focus on managing systems allow the player to choose they challenges they complete, and often even provide a level of engagement, through sheer chaos or otherwise, that rivals even the highest budget games.
Have you played any games in this genre? What are your favorites? Let us know in the comments!