Phong Nha-Ke Bang among world's 25 best national parks

The complex ranked 15th and was the only national park in Southeast Asia to appear on the list compiled by TripAdvisor, which takes into account the quality and number of traveler reviews and ratings published on its website over a 12-month period.

"The karst formation of Phong Nha-Ke Bang National Park has evolved since the Paleozoic some 400 million years ago and so is the oldest major karst area in Asia," the world's most popular travel guide and review website said.

"Subject to massive tectonic changes, the park’s karst landscape is extremely complex with many geomorphic features of considerable significance. The vast area contains spectacular formations including 65 kilometers of caves and underground rivers."

Established in 2000, Phong Nha-Ke Bang is frequently referred to as the "Kingdom of Caves" for the magnificent specimens it hosts.

The 900-square-kilometer national park, which UNESCO labeled as a global heritage site in 2003, is home to over 300 caves and grottoes that date back some 400 million years.

Around 30 caves are now open to visitors, which have created a tourism boom and given much-needed revenue to the once war-torn province.

Serengeti National Park in Tanzania topped the list, followed by India's Jim Corbett National Park and Maasai Mara National Reserve in Kenya.