Though it will not be possible to explore every tunnel in just one day, you can experience the feeling of being underground the Cu Chi tunnels through guided tours that usually last half a day. Most tourist packages include a guided tour in the Cu Chi tunnels so you won’t have any problems when booking one.
Underground, you should not miss the hospitals, the underground factories, and the underground villages that once housed both the civilians and the Viet Cong. You will surely feel the struggles and the challenges felt by the Vietnamese while living underground and while protecting themselves from the continuous bombings and the wars which broke out.