The Escape-bunker of Stichting IJssellinie (opened 2025) takes place in an authentic 1950s anti-aircraft bunker on the estate De Haere near Olst, part of the real IJssellinie: the 120-kilometre Cold War defence line (1953–1968) from Nijmegen to the IJsselmeer. As bunker crew, you have sixty minutes to execute a battalion order amid low light, thick concrete, ammunition, and camouflage. This is heritage programming run by volunteers, not a commercial escape room: open about five weekends a year, four time slots daily, maximum six players for €95 per group—and slots sell out fast. Regional press raves about the wow-factor of the authentic bunker; the caveat is that in 2025 all 32 teams finished within the hour, suggesting modest difficulty, and the bunker doesn't appear on escapetalk or TripAdvisor.