http://www.towermuseumbassingbourn.co.uk/

That link will take you the tower museum in Bassingbourne England.
That field was home to the 91st Bomb group which just happened to have
the Memphis Belle as one of the planes in the group.
They say it is the only tower of it's kind left.
My dad flew a few missions as a waist gunner on a B-17 with the 91st.

There is also a replica of this type of tower at the Wright Patterson
Air Museum in Dayton, Ohio