The longest railway tunnel and is highest in Thailand. With a length of 1352.15 meters above sea level and 550 meters. Located in the National Park Doi Khun Tan. Construction began on the 2450 B.E., Census in 2461 B.E., which took a long time to buildup to four reigns, By the beginning of the reign of King Rama 5 Completed in reign of King Rama 8. (It takes 11 years to build.) By a German engineer named Emil Eisenhofer controls the whole construction.