A somewhat copy of Chrono Triggers Lavos? I mean in Chrono Trigger Lavos' outershell holds the real beast inside. The Garuberk Tower holds Dark Force itself at the highest chamber, which in my opinion I believe that the top of the tower is the torso of the beast while the whole tower is the body, which it most likely maybe but thats just my opinion on it
Hm, there is a bit of a parallel, but I don't really consider it a copy. Now, if there was some kind of fight at the entrance to the tower, which created a door to the inside... that would definitely do it.