Some of the Amerviet War's most interesting skirmishes took place in tunnels, and the fascinating tunnels at Cu Chi, 55 km outside of Saigon, are easily accessible via a half day tour.
You'll want to insist on seeing the real thing at Ben Dinh, a renovated subsystem of the huge network of tunnels at Cu Chi.
Here, you can see maps and diagrams that display the incredible expanse, life systems, and security systems of the tunnels.
Your guide will show you ventilation holes, tiger pit traps, and a fascinating exhibition of the deadly spiked booby traps laid by Viet Cong fighters.
To get a feel for the tunnels themselves, you really should go in yourself.
Almost anyone of moderate western build can venture inside, and the claustrophobic feeling is limited by small, non-intrusive guiding lights. You can exit after 30 meters, but can go down one more level for another 70 meters if you wish.
The discomforting aspect is shuffling through on bended knees.
One gets an appreciation for the fact that Viet tunnel veterans often shuffled 5 km this way to get to the nearby U.S. base, where they repeatedly stole weapons while U.S. troops were sleeping.
The Ben Dinh complex also offers you the opportunity to fire Vietnam-era armaments, from AK-47s to M-60 machine guns, at 15,000 VND a bullet.
If you hit your target, they even give you prizes.
Tom Mangold and John Penycate's sobering Tunnels of Cu Chi (1985, ISBN 0-425-08951-7) is the best book on the subject; read it before you go, if you can.
Book your tour through Vietnam Oasis, and you might have the opportunity of being guided by veteran Mr. Binh Le Thai.
Mr. Binh is alternatively cranky, angry, and joking, passionate about his country, demanding of his listeners, and everything we think a guide should be: informative, opinionated, and lively.