Colonies are the core of RimWorld. They are the central base of operations for all colonists, allowing them a safe place to sleep, grow food, stockpile resources, trade with outside parties, research new technologies, and defend themselves from attackers. Without a well-designed colony to support them, your colonists will be left to the mercy of hunger, disease, marauding raiders, and even worse threats. This page is dedicated to colonies, especially colony placement and design.
Types of bases
In RimWorld, there are three types of colonies: underground bases, open ground colonies, and hybrid colonies.
Underground bases are colonies which have been built into a mountainside. The most prominent benefit of this is that enemies can only approach the base from its exterior entrance(s). This makes it highly defensible. It also means less exposure to the outside elements when dealing with especially hot or cold biomes. However, it also makes it trickier to obtain certain resources such as food and wood -- you may be forced to rely on hydroponics in certain inhospitable conditions.
Open ground colonies are built out in the open. The benefit of this is that they can be built anywhere, rather than requiring specific natural features to be built into. However, they require much more defending and are more susceptible to raider or mechanoid attacks.
Hybrid bases have some features of the two previous styles, mixing and matching according to the builder's needs.