Its a great place to realize history. I recommend to go there on summers (Feb-April). If you can, unless you're claustrophobic, do try to go down the tunnels and always bring a small flashlight of your own. Its a once in a lifetime experience. Be prepared for high humidity around the forest and in the tunnels. Bring your own drinking water and anti-insect lotion if you want.
You can arrange a tour from your hotels in the city.
Its quite easy to get lost in that town when you only got a taxi off the city street. Try to go on mornings, its about 1.5hr drive from District1 of Ho Chi Minh city. Do take tons of photos here and at the garden with Pagoda / Shrine at the left side before going out of the area.