There is this place under metrica province which no one can get to. The zone is unnamed and is part of the tarnished coast. Is it part of the ring of fire?
Another zone is blood legion homelands. These are places I have no idea how to get to them. I own both path of fire and path of thorns expansions. I do have some parts of the ice brood saga story done.
There are also tons of other mysterious places. Woodland cascades, the wall in the sea covered in green vines next to caledon forest, unwnding ocean.