VIETNAM
Cu Chi Tunnels
Two hundred and fifty kilometres of it, most of it very small
1 way to do it, all bookable here
The tunnel network northwest of Ho Chi Minh City ran to roughly 250 kilometres at its greatest extent, on three levels, with kitchens, hospitals and sleeping quarters dug into them. Sections have been widened for visitors and are still a tight, hot crawl; there are exits every twenty metres or so for anyone who has had enough. The trapdoors and the improvised weapons are the part that stays with people. It is a half-day from the city, and it is a war site rather than an attraction.