Same! For me it was the outposts and buildings. By the time we stopped playing I'd paved half our discovered area with roads, built way stations so you could sleep while traveling, and had a base and dock on every important island or biome.

My crowning achievement was called The Sky Vault. I'd lifted 4 pillars to the maximum terrain hight on a tiny plains island, then built a building supported by them that could only be accessed via portal. There I had a long table and thrones for each of us and a collection of all the treasures, cool trophies, and artifacts from out time in play. Covered the room in piles of gold, little chests, cool weapons that we didn't end up using. The finishing touch was that the gate to our settlement stood between two of the pillars, so you got to walk under it get into the town.