The centre will organize an international mountain climbing contest at the end of the month.

The Dark Grotto, which belongs to the Phong Nha Cave system, is 5,258m long and 80m tall and is home to thousands of stalactites in various shapes and colours as well as several indigenous species of bat and swallow.

The centre says two zip line routes will start operating in the park from next month with one route connecting the animal conservation station and Toi Cave, which is about 350m long.

The other 100m route, which crosses the Chay River, can be used by tourists who want to swim in the clear and cool waters of the river. Tourists can also indulge in fun acrobatics along the route.

This Tet (Lunar New Year) festival marked the reopening of Tien Son Cave to tourists, after a 10-month tourism renovation project at the cave.

The mouth of Tien Son Cave is 1,000m from the mouth of Phong Nha Cave which is also known as the Water Grotto or Lower Phong Nha while Tien Son is known as the Dry Grotto or Upper Phong Nha.

During the first four days of the Tet, the park received more than 3,000 tourists, including more than 500 foreign tourists.