The tunnels were dug with simple tools and bare hands during the French occupation in the 1940s, and further expanded during the Vietnam War in the 1960s to provide refuge and a defensive advantage over the American soldiers. Despite all the bombings in their town, the Cu Chi people were able to continue their lives beneath the soil, where they slept, ate, planned attacks, healed their sick, and taught their young. Some even wed and gave birth underground, but over 10,000 lost their lives here.
A multitude of tour buses leave Ho Chi Minh City for the Cu Chi tunnels daily. Expect to pay around US$5 for a half day guided trip (not including admission to the tunnels), with 90 minutes travel and about an hour and a half touring the area. Buses mostly leave around 8:00, so consider a private car if this isn't suitable. Tour operators on Phan Dinh Phung will quote from $35 - $50 return by private car, or possibly lower -- don't be afraid to shop around.
If you're making the trip independently, hop on bus 13 from the Ben Thanh bus station. The last stop on the route is Cu Chi. Bus fare is 7,000 VND, and the ride is about 1.5 hours. When you arrive at the Cu Chi bus station negotiate a motorbike driver for the 20-minute ride for around 100,000 VND return (pay attention as starting price could be 200,000 VND or more). It is also possible to take bus 79. Ask the driver for Cu Chi tunnels, the ride will last about 45 minutes and cost 5,000 VND. The bus will reach a T-junction with Ben Duoc on the left and Ben Dinh on the right. Get off at this point and walk on to Ben Dinh, or stay on the bus as it drives right pass the Ben Duoc entrance. Warning, the buses are sometimes very warm and crowded but manageable.
Admission to the tunnels is 80,000 VND as at May 2012, which includes a guide who may or may not speak English well. While friendly, these guides may attempt to rush the tour or distance you from paid guides/groups -- just indicate that you aren't ready to move on yet and take your time if you feel you're being rushed.
There are actually two locations frequented by tourists:
A well defined walking track loops around the area, with things to see spaced at regular intervals, including examples of how people lived and what they ate. There is a 30m section of tunnel which visitors can crawl through (not recommended for the claustrophobic), examples of traps used during the war, and the remnants of bomb craters. Warning: Many travellers put themselves into small ventilation holes for phototaking. It is great fun but consider your body before getting in as some had difficulties getting out and had to crawl to the exist point.
There are numerous souvenir shops at the end of the walking track. Given the location there is some focus on war memorabilia, as well as the traditional Vietnamese souvenirs found elsewhere.
There are a number of stalls selling food and drinks near the entrance. Mid-way around the walking track is a kiosk/restaurant selling drinks and food and ice-cream at reasonable prices, and at the end there are samples of traditional "Tapiaco (Asian Potato)" to try.