Dong Hoi, Vietnam
More than 300 caves and grottoes can be found in Phong Nha-Ke Bang National Park.
The park is home to the oldest limestone caves in Asia, including Han Son Doong which has a ceiling twice the height of Big Ben.
Dong Hoi is about to be transformed into an international seaport with investment of $800 million into its harbour.
During the Vietnam War, Dong Hoi was on the frontier between North and South Vietnam.
Dong Hoi is on the edge of the Demilitarized Zone: an area of huge importance in the Vietnam War.
Phong Nha-Ke Bang National Park was named a UNESCO World Heritage Site in 2000 for its unique karst landscape.