Nam Son Grotto is one of the nicest grottoes of Hoa Binh Province. It was discovered in 2002 in Ton village, Nam Son commune, Tan Lac district, Hoa Binh Province. From the foot of the mountain, visitors will have to climb over 300 metres to reach the grotto which is halfway on the mountain. Century-old trees along the access make the landscape more peaceful; the higher one gets the more spacious and airy one feels.

Standing at the entrance, visitors can enjoy the panorama with high mountain, vergin forest and a deep cave, wrapped in clouds, fog and dripping water all year round. The grotto is 400 metres in length. It goes across the mountain at the average height of more than 50 metres (20 metres in width). Deep inside the grotto are pools of very clear and smooth water. The stalagmites look so spectacular and when touched by anybody they will produce boisterous brouhaha sounds of a world of gongs. After 2 hours exploring the inside of the grotto, tourists may come out to visit villages at the foot of the mountain, contemplate the dreamful landscape of mountains and waters and will certainly be amazed and impressed by the marvelous grotto of Nam Son.