RimWorld's new Odyssey DLC introduces new systems not found in the base game, and Landmarks are a prime example of this.
In Odyssey, you're no longer stuck on a single planet with the objective of having to build up your ship and escape. Instead, you have your Gravship, and that allows you to explore space with your crew. When you touch base on the map, you'll come across Landmarks, which are essentially pre-existing systems that are now abandoned.
