West Tours, Aðalstræti 7 (tel. 456-5111; www.westtours.is), the dominant tour operator in the Westfjords, is highly recommended and has an imaginative range of offerings, from bird watching and sea kayaking to fox-spotting and berry picking. A particularly exciting day tour is the 12-hour boat and hiking excursion to Hornvík in Hornstrandir Nature Reserve. West Tours rents mountain bikes and can suggest fantastic routes, such as the coastal road around the peninsula between Arnarfjörður and Dýrafjörður. Some tours are for groups only, but it's worth asking about any scheduled group tours you could sign on with.
In winter, options are abundant, particularly for cross-country or backcountry skiers.
Hiking -- The “Ísafjör[ður-Dýrafjörður” trail map (part of the Vestfirðir & Dalir map series), sold for 1,400kr at bookstores and the tourist information center, thoroughly outlines local trails, including distances and difficulty ratings. A pleasant short hike (about an hour round-trip) starts from Route 61, directly across the fjord from the southern tip of Ísafjörður and ascends 220m (722 ft.) along a creek to Naustahvilft, a bowl-like indentation in the mountainside (Icelanders call such formations "troll seats"). A recommended all-day hike (20km/12 miles; 8 hr.) starts from Ísafjörður's northern suburb Hnífsdalur, ascending Hnífsdalur Valley before descending through Seljalandsdalur valley and back into town. A municipal bus (schedule at www.isafjordur.is) goes to Hnífsdalur several times daily (7:15am-6:45pm). An equally recommended and somewhat less grueling hike (16km/10 miles; 6 1/2 hr.) starts by a bridge at the base of Skutulsfjörður and ascends through Engidalur valley along the Langá river past a hydroelectric power station, with a detour to Fossavatn lake.