Úlfarsfell is the smaller, easier neighbour of Esja, rising 295 metres just southwest of Mosfellsbær. From the car park at the foot of the hill the marked path winds up through volcanic gravel and lichen to a flat summit cairn — an hour up, less down. Local families and runners use it as an evening workout, and on weekends you'll meet dog walkers, trail-runners and the occasional skier in winter.
The reward at the top is a 360-degree view: Reykjavik laid out to the southwest, Mount Esja directly across the valley, and the geothermal plumes from the Hellisheiði power station on the eastern horizon. There are several marked routes up and down, so it is easy to make a loop. Bring a windproof layer — the summit is exposed and a steady breeze blows even on calm days in the valley.