I have "finished" the game and keep thinking I've explored everywhere. But then I'll go for a wander and discover some new places/buildings that I've not been to before.

I have finally met all the companions, I only went to find Cait and Curie after finishing the main story.

Unlike seemingly everyone else I didn't travel much with Dogmeat, as Codsworth made a far more useful (if sometimes annoying) companion early in the game.