Just south of Chiang Mai is what’s often referred to as the ‘Grand Canyon’; well it’s sandstone colour and looks a bit like the other one I guess… There is a restaurant (Tung Tong) overlooking the canyon, and otherwise you can enter the site from the other side.
See Chiang Mai: Driving Routes for directions.
Swimming is not advised and may actually be banned; this place has claimed several lives in recent years.
