This placeI imagine this place to be the ancestral home of a priest-ruler, with underground cells (or a lab?), a burial gallery (or vault?) and a sacrificial room with an bottomless pit. Now a ruin, the site has seen a couple of different inhabitants. The caverns or excavations on the right hand side were perhaps made by monsters or barbarian invaders.
A: One story gatehouse on the grand staircase, with many arrowslits (could bear improving, better version in B) and stairs to the underground structure.
B: Elevated palazzo, throne room, bell tower. Arrowslits came out better here.
C: Caves (or digging) breaking into the main structure. Lower cave opens up on the bottomless pit. Probably whatever made them was either from the surface and looking for buried treasure, or from below.
D: Your basic underground lab / prison / vault / sacrifice site.