There are a number of ingredients that make a good site to explore-
Mold and fungi
and finally – dead birds
These little critters are found in most of these places and come in various varieties and states of decay.
I remember one place having a large room full of the complete lifecycle of pigeons-completely mummified ones on the floor, some flapping around in the last throws of life and chicks high up in the rafters in nests. It was an incredible place.
Here are a few I have gathered over the years