Czech Republic, great place to go. Went to a place called Namest a few years ago, one of the things noticed was that when the Russians and WarPac members built their HAS, they based them on the aircraft prevalent at the time. When the Mig-29 and Su-24 and 27 came into service, they were too big to get into the shelters. NATO HAS, 3rd generation ones anyway, were built with aircraft size in mind. Looking at the early ones though, easy for F-104s, bit of a squeeze for a Tornado or Typhoon though!!!
Caslav and Pardubice amongst others are former Luftwaffe bases from WW2, and when I saw them still had, what appeared to me, remnants of that architecture, as did Brno and another place I drove past whose name escapes me at the moment.