Hang Toi (Dark Cave) is located within Quang Binh Province's Phong Nha-Ke Bang National Park.

Discovered in 1990, the cave boasts a primitive beauty with thousands of spectacular stalagmite and stalactites. 

Here are some photos taken during a tour to explore the site.

Through the two-day and one-night tour, visitors travel through the forest and explore Sinh Ton (Survival) Valley, E cave and Thuy Cung (Aquarium palace) Cave while crossing through the 6-kilometre Toi Cave. (Photo: VNA)

The tour begins with the exploration of E Cave, located deep in the park’s thick forest and covered by a unique stalactite system. (Photo: VNA)

The next stop is Sinh Ton Valley, which is well-known for its century-old trees and unique flora and fauna such as flowers, mushroom, monkeys and multi-coloured butterflies. (Photo: VNA)

Arriving at Thuy Cung Cave – the back gate of Toi Cave – visitors set up tents, have dinner, rest and experience an exciting night in the forest with games and art performances. (Photo: VNA)

Inside the cave is a long golden sand strip. (Photo: VNA)

Discovered in 1990, Hang Toi has a primitive beauty with thousands of spectacular stalagmite and stalactites. (Photo: VNA)

Tourists can reach Hang Toi by a 400m zip-line from an observation deck. (Photo: VNA)

The cave was formed about 5 million years ago with stunning beauty. (Photo: VNA)

The 5,558m long and 80m high Hang Toi is a shelter of many species of animals like bat and swift. (Photo: VNA)

 (Source: VNA)