The largest teak tree in the world stands in Ton Sak Yai National Park. The tree, estimated to be more than 1,500 years old, is 37 meters high and has a circumference of 9.58 meters at its base. Although the upper part of the tree was broken off in a storm, the trunk is still alive and well-cared for. Found in 1927, the giant teak tree is part of the 35 square kilometer park of mixed deciduous forest. A two-kilometer trekking route allows visitors to explore the forest firsthand.
Ton Sak Yai National Park is about 92 kilometers from Uttaradit City via Highways Nos. 1045, 1146 and 1047, past the entrance to KhlongTron National Park. The drive passes through deciduous dipterocarp forest and teak forest, where the leaves change into beautiful colors during the winter months. On the way back, it is possible to make a detour through the forest along the road to Sirikit Dam and ThaPla, before returning to the main road to Uttaradit.