Thung Nai — "the Valley of Deer" in the Muong language — was a forested valley before the Hoa Binh Dam flooded it in the 1980s. Today it is the most scenic part of the vast reservoir: about 47 limestone islands rising from calm green water, draped in jungle, with Muong fishing villages clinging to their lower slopes. Vietnamese tourism has taken to calling it "Ha Long Bay on land," which is a stretch, but the scenery is genuinely striking. The best time to come is autumn, when the reservoir is at its fullest and the water reaches deepest into the valleys.
You reach Thung Nai — about 25 km from the city — by road and then by boat from the wharf. From the water, you can visit Coconut Island, call in at Mu or Gia Mo village to see how local families live on the lake, and continue to Thac Bo Cave, a karst cave on a peninsula that has been recognised as a national heritage site. The cave itself is over 100 metres deep, with three large chambers decorated with stalactites. Boat hire for a morning circuit of the main islands is straightforward to arrange at the wharf.
story: > The name "Thung Nai" preserves a memory of the valley that vanished. Muong villagers who were displaced by the dam's reservoir still use the name — the valley of deer — for water that now covers what used to be their home. A few families resettled on the island slopes; their stilted houses sit at the waterline, and they fish the same stretch of river their grandparents farmed.