Chae Sorn National Park in Chiang Mai & Lampang
Chae Sorn National Park is on the mountain tops of the border between Chiang Mai and Lampang province. Sorry the stunning photo is not from myself but from the informative website Thailand Nature Travel
For hiking in this wonderful area see also Green Trails The main attraction of the park are hot-water springs and a 6-level waterfall. Be aware that they charge an entrance fee per person and for your motorbike (or car).