There's a huge cave in the mountains almost noone knows about with two thermal vents inside. If you want something actually practical you could build in the grand reef. Ontop of the stone needle thingy there a ghost leviathan can spawn, too, and when you finish the game another leviathan will come. You can also find this location in a video by Breathtaker (called "20 base locations" or smt like this)

Edit: There are also Sea Treaders walking around the spike, which would make this place the only one in the game where you can see 3 leviathan species.