Some cracked walls would go a long way. Perhaps some parts of the walls caved in, exposing the outer cave within the crypt. Cracked walls leave debris, perhaps some near the walls. Floors crack over time or have a layer of dirt/dust etc. on them. Some wood used as support at a later stage in the crypt to ensure that the ceiling does not collapse, so it would look a bit out of place but then again, it would fit perfectly if you can execute it in a way that people would actually recognize it as such. Maybe some weeds/green in a place that is moist. Maybe some belongings from the deceased?
Put some monster spawns in there, open up tibia and play through it. Does it feel empty or just right? I mean, all the items that players would drop on the ground, all the creature bodies that are decaying over there. This adds up to the "details" as well.