As mentioned above, Víknaslóðir: Trails of the Deserted Inlets is essential for exploring the region. Trails are well-marked from the main road, and a map is posted at each trailhead. The best time for hiking is from early July to early September, though many routes are clear of snow by June. In late August you can eat your fill of krækiber (black crowberries) -- keep an eye out for the rare albino variety. The weather is rainier in September, but you'll have plenty of solitude.
The best trips in Borgarfjörður Eystri last two to 7 days, but if you have just 1 day (and no access to a 4WD vehicle), the two best day hikes are to Stórurð and Brúnavík. Both destinations take around five to 6 hours round-trip.
Stórurð is a mystical jumble of oddly shaped boulders around a blue-green stream and pond with grassy banks. Don't come before early July, when the snow lifts. The best trail route (marked #9 on the Víknaslóðir map) starts at the 431m (1,414-ft.) Vatnskarð pass on Route 94 west of Njarðvík, and crosses the 634m (2,080 ft.) Geldingafjall peak before descending into Stórurð. This trail has some ankle-twisting stretches of loose gravel and scree. Somewhat easier trails (#8 and #10) reach Stórurð from different parts of the road, but #9 has the best approach to Stórurð, as well as astounding views of Njarðvík, Fljótsdalshérað Valley, and even Snæfell and Vatnajökull. You could return by one of the easier trails, but would have to walk back to your car along the road.
Brúnavík, the first cove east of Borgarfjörður, has a lovely beach of rhyolite sand and was inhabited by two families until 1944. Two trails lead to Brúnavík from the coastal road on Borgarfjörður's eastern side. For the optimally dramatic descent into Brúnavík, the best circular route is clockwise, heading to Brúnavík through the 345m (1,132-ft.) Brúnavíkurskarð Pass (the trail marked #19 on the map) and returning through the 321m (1,053-ft.) Hofstrandarskarð Pass (trail #20).
The trails and Jeep tracks -- and the best multi-day trips -- extend all the way south to Loðmundarfjörður, or perhaps even to Seyðisfjörður. Loðmundarfjordur had 87 residents at the outset of the 20th century, but the last ones left in 1973, after failing to convince authorities to build a road around the coast from Seyðisfjörður. A partially restored 1891 church is still standing but stays locked up. (Húsavík also has a cute church near the ocean; it dates from the late 1930s and always remains open.)
The scenic highlights of Borgarfjörður Eystri are manifold, but Hvítserkur should be singled out, as many consider it the most strangely beautiful mountain in Iceland. The main bulk is pale-rose rhyolite, but glacial erosion has exposed dark basaltic ribbons that look like paint splattered by Jackson Pollock. Hvítserkur's best side faces south, and can be seen from Húsavik and the 4WD road leading there.
Note: This information was accurate when it was published, but can change without notice. Please be sure to confirm all rates and details directly with the companies in question before planning your trip.