Cu Chi Tunnels.
These war-time Vietcong tunnels are a must, even if a tad theme park. Book a car and driver, and pick up a tasty deli lunch at Annam Gourmet Market (see V. Useful, the food out of town is limited). Tell your driver you wish to go to Ben Dinh Tunnels (the Ben Duoc tunnels are tourist reconstructions) and allow half a day. Stop by the Cu Chi Wildlife Rescue Station / 3794 7045 / 7.30-11.30am & 1-4.30pm / call ahead / wildlifeatrisk.org / rehab for animals confiscated from illegal trade. For a full, hot and rather bumpy day, proceed to Tay Ninh to see the Cao Dai Temple. The interior designer here was clearly Liberace, or on drugs, or possibly both. Exotissimo (see V. Useful) offers a fun variation by boat or with a war vet guide.