This is how Vietnam won the war: An immense network of underground tunnels. When the Americans began bombing the villages of Cu Chi, thousands of the survivors went and lived in an elaborate system of underground tunnels.
The touristy part of the tunnels is well lit. It’s still not recommended for the claustrophobic people though.
The whole area has been turned into some kind of war memorial park and you’ll find all the Vietnam War related displays.
Side trip: If you are in the mood for some temple run you might want to visit Cao Dai temple & learn about this fascinating homegrown Vietnamese religion before going back to HCMC.