Navigation charts / maps
I had one of these (in paper form) years ago of the UK but it's disappeared in the mists of time. However, today I stumbled across a massive collection of navigational charts, all scanned-in very nicely. They date from post-war to the ~90's, perfect for planning a cold-war era route! Lots of airfields now decommissioned and becoming housing estates / business parks are shown, along with navaid info etc...
Thanks to the University of Texas for hosting them.
Operational Navigation Charts:
https://maps.lib.utexas.edu/maps/onc/
Tactical Pilotage Charts:
https://maps.lib.utexas.edu/maps/tpc/
Lovely stuff.