Khun Tan Tunnel

Its length is given several ways: most Thai sources, including Silpa Watthanatham and Lamphun province, say 1,352.10 m, while a 2018 Burapha University study and the kilometre markers give 1,362.10 m. The bore is 5.20 m wide and 5.40 m high, arched and lined with reinforced concrete; over 60,000 m³ of earth and rock were removed.

Boring began in 1907, late in Rama V's reign, and finished in 1918 under Rama VI, about 11 years and roughly 1.36 million baht funded by foreign loans. It was designed for standard gauge and later used for metre gauge, leaving generous clearance. No formal opening date has been confirmed; claims of 1 January 1918, 1921 or 1925 lack support.

Silpa Watthanatham has published two old photos: an inspection by the Minister of Communications in 1911 and a royal visit at the north portal in 1916, whose caption does not name the visitor.

The boring from 1914 to 1917 was directed by Emil Eisenhofer (1879–1962), a German engineer with a firm hired by the Siamese government, who suffered malaria on the job. When Siam declared war on Germany in July 1917 he and other German engineers were arrested, held about six months, then interned in India for about two years before returning to Germany in 1920; Thai engineers finished the work.

Eisenhofer returned to Thailand in 1929 and lived there until his death in 1962. His ashes rest in a small stupa near the portal by Khun Tan station, built by the railway as a memorial. In front of the tunnel is the shrine of Chao Pho Khun Tan, where people pay respects before travelling.

Locals called Eisenhofer "Mr. Hofer". His wife is buried with him at the memorial by the north portal. He also built Ban Pin station in Phrae, which opened in 1914.

Several groups did the work: Silpa Watthanatham says Chinese labourers handled the earthworks while Shan and Isan workers drilled the tunnel, and some accounts mention Lao workers partly paid in opium. Workers died of malaria, cholera, dust-related lung disease and tiger attacks, but figures of "over a thousand" or "thousands" of deaths are unverified anecdote.

Silpa Watthanatham says workers received one tube of opium per shift, deducted from their wages and arranged legally through the government of the time.

Before the railway, Bangkok to Chiang Mai by the Ping River took one to two months. Once the tunnel was done, the line ran on from Lampang to Chiang Mai on 1 January 1922, cutting the trip to three nights by ordinary train or about 24 hours by express.

The portal is red brick with a Garuda emblem above the entrance — the only Thai railway tunnel with one, according to Lamphun's tourism office.

Khun Tan station (code KhN.) at km 683.14 sits at about 578 m, often called the highest railway station in Thailand. The original building served from 1918 to 1960; the present one was finished in 1959 and opened in 1960. Black-and-white construction photos are displayed at the station.

Khun Tan was Thailand's longest railway tunnel from 1918 until 28 July 2024, when the 5.41 km Pha Sadet tunnel opened on the Map Kabao–Thanon Chira Junction double track in Saraburi. The Ngao tunnel of about 6.2 km on the Den Chai–Chiang Rai–Chiang Khong line is targeted for around 2028, while a 7,272 m new tunnel near Khun Tan for a Den Chai–Chiang Mai double track was still at the environmental-review stage in 2023.

Rains have brought repeated landslides. On 7 September 2012 a flash flood washed out about 36 m of track between Khun Tan and Tha Chomphu. On 22 September 2024 a landslide at the portal and flash floods halted Lampang–Chiang Mai trains from 23 September, with buses replacing them. On 14 June 2026 a landslide at the north portal closed the line from 17:18 until about 19:40 the same day.

No Second World War event specific to the tunnel has been found, though the Northern Line as a whole suffered Allied bombing. Eisenhofer's arrest belongs to the First World War, not the Second.

The tunnel is an active line: never walk into it or along the tracks. View and photograph it from the Khun Tan platform and the area in front of the portal; it is free and open all day. Special express, rapid and local trains stop at Khun Tan — check times with the SRT on 1690 before you go.