What should I put in my ruin? a GM asks on Facebook. The question is smarter than it might appear. If you are aiming for an immersive, coherent world and an exciting adventure, it can be tough to stock a ruin properly.
Throw stuff in randomly and you might find yourself on the defensive or retconning as players try to make sense of its ecology. Or, worse, they might make reasonable, fatal errors because they expected the dungeon to make some kind of sense that it didn’t in fact make. It may be helpful to think of the ruin as having three or four sections:
the Grounds (the area around the ruin),
the Landmark (the visible part of the ruin that’s easily explored and already well-spoiled by previous visitors),
the Sanctum (a hidden and/or well-secured area that the PCs will be the first to visit),
and, optionally, the Intersect (a place where the site intersects with tunnels or underground realms, creating an opening through which denizens of the Underdark might enter the complex).