When the military closed the site, they 'surface cleansed' the site of unexploded ordnance and stripped out all the buildings. They didn't go below the surface and there are probably tons of uxb's still to be discovered.
Now, the Ness is a nature reserve and visitors are told to stay on the designated paths for obvious reasons and the buildings are usually out of bounds too. However on the day we visited, many of the buildings were open to show off a few bits of commissioned works of art (not my cup of tea) but it was fascinating to see inside the experimental labs, etc.
It's an amazing place and only a visit will do but I attach few photos to give you a flavour.
Spooky, or what?