The UNESCO-recognised global heritage site in central Vietnam ranked 15th and was the only national park in Southeast Asia to appear on the list compiled by TripAdvisor, which took 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 is the oldest major karst area in Asia, according to TripAdvisor. Established in 2000, Phong Nha-Ke Bang is frequently referred to as the "Kingdom of Caves" for the magnificent specimens it hosts. The 900 sq.km national park, which UNESCO labeled as a global heritage site in 2003, is home to over 300 caves and grottoes that date back 400 million years./.