Ahuashiyacu -- "Laughing Waters" in Quechua -- is a 40-metre waterfall tucked into the cloud forest about 14 km from Tarapoto on the road toward Yurimaguas. What was once a grueling scramble over boulders and along cables is now a well-maintained trail with stone steps and footbridges, managed by the regional government. The walk up takes about 20 minutes and is manageable for anyone in reasonable shape, though the altitude and humidity will make you sweat.
The trail ends at a ledge behind the falls where you can get as close as you want -- or as wet. A shallow pool at the base invites a dip, but the water is mountain-cold and the rocks are slippery, so watch your footing. There's a changing area near the trailhead. A small entry fee covers trail maintenance.
Best visited in the morning before clouds roll in. Mototaxis from Tarapoto will bring you to the entrance and wait, or you can arrange a return through your driver.