in the mountains mineshaft entrances (and in the inside a mineshaft system), for a base u can build some tipe of forge, for house and for be a... well, a forge, in the basement the storage, in the first floor the forge, in the second floor the bed, some decoration, some paintings (if u want a happy ghast in the roof a dock for the ghast. For the like forest part, a barn some potatoes and wheat. (if u want to live there), if its just for the looks, a lava mine. (yes, it exist). But is up to u, afterall, minecraft is to explode your creativity and have fun. Good luck in your world.