Things to do in Ranong.

The most famous thing in Ranong and the least likely: a mineral hot spring inside the provincial town, in a public park. The Department of Science Service analysed it and found it to be the only source in Thailand containing no sulphur additives — which means no smell, and water regarded as pure enough to drink at source. It is the reason Ranong markets itself as Thailand's onsen town, and the reason a fair number of Thai visitors come at all. For residents it is simply a place to soak in the evening, which is a genuinely good thing to have at the end of a wet-season week.

A hill entirely bare of trees, covered in grass, twelve kilometres south of Ranong town, in a province that is 53.5 per cent forest and 67 per cent mountain. Locals compare it to a Swiss pasture; the honest description is a geographical anomaly nobody has fully explained. It changes colour with the season and the light, which is why it appears on every photograph of the province, and it is named in the provincial slogan alongside the isthmus, the cashews and the mineral springs.

Ko Phayam is a small island — about two and a quarter square kilometres, eight kilometres at its longest, 350 registered residents at the 2012 count — of coconut and cashew plantations over a hilly centre with beaches around the edge. It has kept a low-rise, motorbike-and-walking character that most Thai islands lost, partly because power has historically come from solar and generators rather than a mainland grid. Ranong's own Ko Chang, eighteen square kilometres and about eighty homes, is quieter again. Note this is not Trat province's famous Ko Chang, which is an entirely different island on the Gulf.

The province's main coastal park, covering the shore and a scatter of Andaman islands. Hat Bang Ben is the long pine-shaded beach where the park headquarters sits; Hat Laem Son runs about four kilometres alongside it, and Hat Praphat — also called Hat Hin Thung — is another wide beach of the same kind. Offshore, Ko Khangkhao has fine sand and a gravel beach known as Hat Hin Ngam at its northern end, and Ko Kam Yai and Ko Kam Nui are white-sand islands with islets scattered around them. This is the part of Ranong that looks like the Andaman coast people picture, without the crowds Krabi and Phuket carry.

Declared a national park on 3 June 1999 and covering roughly 417,500 rai — about 668 square kilometres — of the wet forested hills behind the coast. The waterfall the park is named for is visible from Highway 4 south of Ranong town, which is unusual, and the park is a straightforward day out from the capital rather than an expedition. In a province taking over 4,500mm of rain a year, waterfalls are one thing that is reliably impressive.

The Ngao Mangrove Forest Research Centre, better known as the Ranong Biosphere Reserve, covers 189,431 rai — about 303 square kilometres — in northern Kapoe district. Declared in 1997, it was Thailand's fourth biosphere reserve and remains the only one on the coast protecting mangrove forest. For anyone interested in the ecology of the Andaman shoreline it is the single most significant site in the province, and it is a working research centre rather than a manicured attraction, which is part of the appeal.

The only place in the world where the aquatic plant Crinum thaianum grows wild — an endemic species confined to this stream system, flowering at its best from October into November. That is a genuinely rare thing to be able to say about a place, and it is worth timing a visit for. The sanctuary sits inland in La-un district on the northern side of the province.

A local temple whose draw, beyond the Buddha, is the stream running through it, which holds a large population of rock mahseer that visitors feed. It sits in Hat Som Paen, one of the subdistricts ringing the town, in country that was tin-mining land — the mineral wealth that made Ranong a province in the first place.

Several ferries cross the Pak Chan estuary from Ranong to Kawthaung in Myanmar, a crossing foreigners have long been able to use without a Myanmar visa, and there is also a boat to the island of Thahtay Kyun. It is the reason Ranong is known as a border-run town and it makes for a genuinely unusual day out. Conditions on the Myanmar side have been unstable and the rules change, so confirm the current arrangements with Thai immigration and the operators before going — and do not treat any second-hand account as current.