Hidden treasure?

I'm visiting my son at St. Albans for three days. He took us to a lovely little reserve near his house called  The Watercress Wildlife Association Nature Reserve which is on the site of disused watercress beds and allotments.

It has paths, lakes, an orchard, meadow and bog, a great place for wildlife.
The two men spotted a shed and of course had to peer through the window but there was nothing exciting, just ladders etc.