Doi Khun Tan National Park

Height is the whole point here. The park sits high enough on the Chiang Mai–Lamphun border that the air genuinely changes, and on a hot northern afternoon that alone justifies the drive. It's forested, low-key and nowhere near as busy as the big-name parks, which is exactly why I'd send people who want a walk rather than a line.

The trails vary in difficulty, so you can pick your ambition, from a gentle wander through the trees with a viewpoint stop to something longer and steeper if your legs are willing. Wildlife shows up if you're patient and quiet. Facilities are thin on the ground, so treat it as a proper day out rather than somewhere you'll find a café halfway up. Sturdy shoes, more water than you think you need, sun cover.

Timing matters more than most things. November to February gives you the comfortable temperatures and the clear views. May to October, the rain turns paths to mud and the effort stops being fun.