One of the earliest terrain items I've created, after dungeon walls and some woods and rocks is winter terrain. Having often seen use, this terrain can be used in almost any genre and world; Marines invading arctic base of an evil mastermind, friends of Drizzt adventuring in Icewind Dale, An icy planet to be explored...
Remember the opening scene of Babylon 5 (not the pilot, the actual series), where Narn fleet attacks a Centauri space station in Ragesh III I was sold the moment I saw that, as it made an immediate connection to my favourite PC game intro - Master of Orion 2.
"If there's a center to the universe, then you're on the planet that it's farthest from!"
-Luke skywalker, speaking of his homeworld Tatooine
Addition: I added a few WIP pictures of the buildings to the bottom of the post.