The day after I arrived in Vietnam, I went to the Vinh Moc Tunnels near Dong Ha. I assumed that the infamous Cu Chi Tunnels would be very similar, but there's a huge difference. The people in Vinh Moc were mostly just trying to survive a massive amount of bombing by living underground, but the Cu Chi tunnels were within 50 km of the American stronghold of Saigon so they were almost entirely oriented to smuggling and warfare. People lived in them, but they were set up very differently. I mentioned in the previous entry that the tunnels at sites other than Vinh Moc had been modified, increased in size. Implicit in this (to me, anyway) was the idea that the tunnels were the same size to start with: they weren't. You could sort of walk around in the Vinh Moc tunnels: bent over, but nevertheless. The Cu Chi tunnels were built to be crawled through on your stomach, not even really on your elbows - more like a snake. Sure it was hard to get around, but if an American got in it was incredibly easy to shoot him - if he didn't fall into one of the camouflaged pits full of bamboo stakes first. In Vinh Moc you traverse three levels, see living quarters, a kitchen, and a field hospital (or at least the rooms they were in). No pits full of bamboo stakes. In Cu Chi (at the Ben Dinh site, which we visited), they have about 100 meters of tunnel that have been dug bigger than their original size - no rooms, just one long and incredibly painful crawl/duck-walk. Happily, they have exits every 30 meters for those who don't feel up to doing the full crawl. I bailed out at the first one. Even if I hadn't had my backpack, I'm tall and it was damned uncomfortable.
I should add that there's another tunnel site in the Cu Chi area, at Ben Duoc. This is a full re-creation of the tunnel environment, not original tunnels (although I think there were tunnels there during the war - they probably caved in). The tour I was on didn't include Ben Duoc - I wish it had, as I would've liked to see the living quarters.
The Ben Dinh site also had a very old war propaganda movie about the incredibly peace-loving people of Cu Chi driven to war, and a bunch of demonstration booby traps used to maim American soldiers. Even without live demos it was pretty gruesome - it's amazing what your imagination can fill in. Lots of pits and barbed iron spikes.