Soppong (also sometimes known as Pangmapha, actually the name of the entire district) is a small market village a couple of hours northwest of Pai and about 70km from Mae Hong Son. There's not much to see in town, but the surrounding area is defined by dense forests, rushing rivers and dramatic limestone outcrops and is the place in northern Thailand for caving. The best source of information on caving and trekking in the area is the owner of Cave Lodge in nearby Tham Lot, the most accessible cave in the area.
There are also several Shan, Lisu, Karen and Lahu villages that can easily be visited on foot.
If you're here on Tuesday morning, check out the town's rustic market.