The one I will always remember was working on the refurbishment of a warehouse in East London from 1800s. When we started digging between the foundations, we discovered it was a Black Death pit full of (in some cases) relatively preserved bodies - this is due to the nature of the soil. When they built the warehouse foundations they put the bodies in between the foundations so there was only a thin slab of concrete between 'them' and us.
One of the engineers that I considered a plonker decided to jump into the trench and the bodies fell on top of him. Needless to say, he didn't return to the job - which was fine with me. The guys in hazmat suits took over ..
One of the labourers found a skull and he was just about to play football with it until I restrained him. Some people (eyes roll) ..