Doi Khun Tan National Park straddles the mountainous area of the Khun Tan Range in Lamphun and Lampang Provinces, northern Thailand. Established in 1975 as Thailand's tenth national park, it is an IUCN Category V protected area measuring 159,556 rai~ 255 square kilometres. The park ranges in elevation from 325–1,373 m. Its best known feature is Thailand's longest railroad tunnel, 1,352 m long.