Doi Samer Dao

The name, roughly "level with the stars", comes from how it feels to lie on the open ridge at night when the sky is completely dark and full of stars. Travellers took up the name and it became the park's viewpoint name.

The ridge's story is tied to the birth of Si Nan National Park. In 1989 the Royal Forest Department ordered Sombat Wiangkham, a forest officer from Nam Nao National Park then posted to Wiang Kosai National Park, to survey several national reserve forests in Wiang Sa district — about 435 km² (271,875 rai) — with a further survey ordered on 19 October 1989. At first the area was called "Mae Sakhon National Park", after the well-known headwater forest.

In 1991 the survey was extended to the forests on the right bank of the southern Nan River, Huai Nguang and Nam Wa, covering Wiang Sa, Na Noi and Na Muen districts. On 19 April 1993 Nan province backed the plan, and on 12 January 1994 Forest Department director-general Phong Leng-ee approved a park of about 934 km² (583,750 rai), excluding large villages, and renamed it "Si Nan National Park" because the expansion and a move of the headquarters had made the old name confusing.

On 25 May 2007 a royal decree, published in the Royal Gazette (vol. 124, part 25 Kor), formally declared it Thailand's 104th national park, covering about 640,237 rai (1,024 km²) in Khueng, San and Nam Muap subdistricts of Wiang Sa, Si Sa Ket, Chiang Khong and Sathan of Na Noi, and Bo Kaeo and Na Thanung of Na Muen — following both banks of the Nan River down to the Sirikit Dam reservoir.

The park protects key headwaters of the Nan River, which flows about 60 km through it. Its ranges run north–south, topped by Khao Khun Huai Huek at about 1,234 m. The forest is mostly mixed deciduous and dry dipterocarp, with Irvingia, ironwood, Xylia, padauk and rosewood, and is home to tiger, leopard, wild cats, dhole, mouse deer and palm civets. In 2019 the park had about 115,358 visitors.

On Doi Samer Dao itself, the eastern hill is the "stargazing lawn", good for both sunrise and sunset, with a high cliff looking down over the ranges and the Nan River; the western slope watches the sun set over cornfields. Nearby is Pha Hua Sing, a limestone crag shaped like a crouching lion facing east, with a 360° view from the top — but only with a ranger guide. Visitor reviews say Pha Hua Sing and Pha Chu were once closed for about two years over rockfall risk after an earthquake.

About 4 km away is Pha Chu, another sunrise and sea-of-mist viewpoint, looking down on the Nan River winding through the forest. It is a walk of about 2 km up — roughly an hour there and back — with a ranger guide required. The name comes from a legendary love triangle: Chao Ueang Phueng loved Chao Chan Pha but was forced to marry Chao Chuang, so she leapt from the cliff; Chan Pha followed her, and Chuang, seeing them, jumped too but fell further away. Ueang Phueng became an orchid clinging beneath a chan pha tree, and Chuang a pine — "chuang" means pine in northern Thai and "ueang phueng" is a kind of orchid. The cliff is also said to have Thailand's longest flagpole: the flag only reaches the top after the national anthem has been sung about 12 times.

Near Na Noi town, about 24 km from the park headquarters, are the Sao Din Na Noi earth pillars, also called "Hom Chom", in Chiang Khong subdistrict — strange pillars spread over more than 20 rai, like Phrae's Phae Mueang Phi, formed as uplifted sediments were carved by water, wind and rain. Estimates of their age vary wildly, from about 10,000–30,000 years to several million. On 7 November 1989 the cabinet listed the site as a natural area worth conserving. It is also a prehistoric site where chipped stone tools, stone axes and stone bracelets have been found, now kept at the Nan National Museum, and was the subject of a Silpakorn University study in 2012. On 10 November 1995 Princess Sirindhorn brought Chulachomklao Royal Military Academy cadets here on a study trip. Villagers hold the pillars sacred, and about 800 m away is Khok Suea ("tiger pen"), a deep pit where villagers are said to have driven and killed tigers that preyed on their cattle.

At the park's southern end the Nan River flows into the Sirikit Dam reservoir, where Ban Pak Nai lies in Na Thanung subdistrict, Na Muen. It was once a riverside village, but when Sirikit Dam was built the old village went under the reservoir; settlers from many places moved in and took up freshwater fishing. Today there are floating fish restaurants and pontoon ferries across to Ban Tha Faek in Nam Pat, Uttaradit — which stop when the reservoir runs low, as in July 2021.

Today Doi Samer Dao is southern Nan's favourite campsite. The park is open all year, but camping is allowed only from about 1 October to the end of February. The terraced campsite has two toilet blocks without hot water, power at set hours and no park shop; in season, villagers come up to sell food. The Tourism Authority of Thailand sees Doi Samer Dao and Si Nan as the magnets of "South Nan", and in 2022 developed the "Suk Samer Dao" community route at Ban Nong Pa Kha in Si Sa Ket, where visitors can try award-winning Na Noi robusta coffee, visit the Phra That Si Sa Ket stupa and see Wat Na Tao's scripture library, said to be over 600 years old.

Visitors can help by taking all rubbish back down, not lighting fires or grilling in front of tents, keeping noise and lights down after 22:00 for stargazers, and staying off cliffs and closed areas.