Pokhara is the launchpad for the great Annapurna treks — the Circuit, the Sanctuary, the Mardi Himal, the Poon Hill loop — but for travellers who only have a day or two, there are several worthwhile outings closer to town.
The classic short hike is Sarangkot for sunrise: a 5am taxi to near the top, the last fifteen minutes on foot, sunrise over the Annapurna range from the viewpoint, and a leisurely two-hour walk back down to the lake. The Phulbari–Naudanda ridge walk above the north shore of Phewa is a longer half-day hike with comparable views and fewer people. Begnas Lake, 15km east, is a half-day if you take a boat out, longer if you walk between Begnas and Rupa.
For travellers happy to drive, Bandipur — a beautifully preserved hill town an hour east — makes a good day trip, as does Tansen (Palpa) for serious old-Nepal architecture, though both are more rewarding as overnights.