There's a huge, intricate tunnel network outside of Saigon, known as the Cu Chi tunnels, that was used extensively by Viet Minh/Viet Cong forces during the French and American wars. Imagine an ant farm, with all of its routes and levels, for humans -- it's a pretty incredible display of labor and determination: the tunnels totaled over 200km in length, over multiple stories, and included features such as medical rooms, sleeping rooms, and underwater entrances with trapdoors.

Trapdoors were also the way in and out of the tunnels -- small and concealed by brush, they made it easy for the Vietnamese to disappear in mid-pursuit. Not all of the trapdoors were entrances, though; the guerillas also developed a large assortment of booby traps, samples of which are on display at the tunnels.

Pretty much all of the traps involve some form of lever or pivot, and spikes that come hurtling or snapping at you (or you into them, as at right); you can probably figure out the differences from their names. There are the clipping armpit trap, the door trap, the leg trap, and the window trap, among others. I forget the name of this one, but it's basically a see-sawing floor trap. Guess what's on the other side of the leaves -- yep, lots of pain.

Most of the network was pretty well bombed out by the end of the American war, but portions have been reconstructed and opened to tourists. Our group of about 15 was given the opportunity to traverse what I think was 100m of tunnel. A few of the more claustrophobic (or injured) chose the surface route, while most at least descended to see what it was like, but exited at one of the first two (of four) opportunities. The tunnel we entered started out as you see in the picture -- probably a bit under four feet tall, and reasonably wide. With a line of people between you and the exits, it was uncomfortably hot and humid, and that's coming from someone who likes heat and humidity. By the time we reached the last 20m, there were only four of us still remaining in the darkness (the guide had gotten too far ahead and taken the light with him), crawling in a much more compressed -- both narrower and shorter -- space. There were Vietnamese soldiers who spent months in those tunnels, but it took no more than five to ten minutes for some members of our group to start freaking out.