The tunnel network used during the war is 70km from HCMC. Most tours combine it with a Cao Đài temple visit.
The 'tourist tunnel' is widened for visitors but still claustrophobic. If you're large or panicky in tight spaces, skip the crawl.
Go early (8 AM departure) to beat the heat and the largest tour groups. Book through your hotel or via Klook for around $20–30.