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Designated a Unesco World Heritage Site in 2003, the remarkable Phong Nha-Ke Bang National Park contains the oldest karst mountains in Asia, formed approximately 400 million years ago. Riddled with hundreds of cave systems – many of extraordinary scale and length – and spectacular underground rivers, Phong Nha is a speleologists’ heaven on earth.

With limestone outcrops amid serene rice paddies, Tam Coc is best appreciated on a languorous rowing-boat ride, with the soundtrack of the river lapping against the oars.

The site of Vietnam’s most extensive Cham remains, My Son enjoys an enchanting setting in a lush jungle valley, overlooked by Cat’s Tooth Mountain (Hon Quap). The temples are in poor shape – only about 20 structures survive where at least 68 once stood – but the intimate nature of the site, surrounded by gurgling streams, is still enthralling.

Lao Cai is squeezed right next to the Vietnam–China border. Razed in the Chinese invasion of 1979, most of the buildings here are modern. The border crossing slammed shut during the 1979 war and only reopened in 1993. Now it’s a bustling spot fuelled by growing cross-border trade.

Once upon a time, Mui Ne was an isolated stretch of shoreline where pioneering travellers camped on the sand. Times have changed and it's now a string of beach resorts, which have fused into one long coastal strip. These resorts are, for the most part, mercifully low-rise and set amid pretty gardens by the sea. The original fishing village is still here, but tourists outnumber locals these days. There are a handful of luxury hotels (and a smattering of cheap guesthouses) but Mui Ne is mainly a midrange resort.

A large, prosperous coastal city, Quy Nhon (pronounced ‘hwee ngon’) boasts a terrific beach-blessed shoreline and grand boulevards. Its seaside appeal and tidy, litter-free streets make it the kind of place that affluent Vietnamese couples choose to retire to, spending their final days ocean-gazing and promenade-walking.

Isolated from the mainland, the Con Dao islands are one of Vietnam's star attractions. Long the preserve of political prisoners and undesirables, they now turn heads thanks to their striking natural beauty. Con Son, the largest of this chain of 15 islands and islets, is ringed with lovely beaches, coral reefs and scenic bays, and remains partially covered in tropical forests. In addition to hiking, diving and exploring deserted coastal roads there are excellent wildlife-watching opportunities, such as the black giant squirrel and endemic bow-fingered gecko.

Meo Vac is a small but charming district capital hemmed in by steep karst mountains and, like many towns in the northwest, it is steadily being settled by Vietnamese from elsewhere. The journey here along the spectacular Mai Pi Leng Pass, which winds for 22km from Dong Van, is the main attraction. The road has been cut into the side of a cliff with a view of rippling hills tumbling down to the distant waters of the Nho Que River far below. Right at the top of the pass is a lookout point where you can stop to take in the scenery.

Most of the bases and bunkers have long vanished, but this 5km strip of land on either side of the Ben Hai River is still known by its American War moniker: the DMZ. From 1954 to 1975 it acted as a buffer between the North and the South. Ironically, the DMZ became one of the most militarised areas in the world, forming what Time magazine called ‘a running sore’.

Wow, the vistas. This is Vietnam's big-sky country; a place of rippling mountains, cascading rice terraces and the winnowed-out karst topography for which the region is famed.