The Pardi Khola, a small river draining Phewa Lake, plunges 30 metres into a sinkhole and disappears into a limestone cave system on the southern edge of Pokhara — one of the more dramatic geological oddities in the city. The viewing platforms get you close to the lip; in the monsoon (June to September) the volume is impressive, in the dry season it's a more modest trickle.
Across the road is the Gupteshwor Mahadev Cave, where you can descend a staircase into the same cavern system to see the river thundering through from below. The two together make a half-hour visit. A small entrance fee for each; both can get busy with Nepali tourists at weekends.