Hiking -- Icelandic Mountain Guides (tel. 587-9999; www.mountainguide.is) leads epic, unforgettable treks off the beaten path, including Askja to Nýidalur in 6 days (65,900kr/$1,054/£527) and Nýidalur to Eldgjá in 7 days (72,900kr/$1,166/£583). Plan on carrying a heavy pack.
Horseback Riding -- Eldhestar (tel. 480-4800; www.eldhestar.is) offers an 8-day Sprengisandur traverse with 6 days spent on horseback (155,313kr/$2,485/£1,243), while Íshestar (tel. 556-7000; www.ishestar.is), an equally experienced and reputable company, tackles the route in 12 days with 9 in the saddle (227,500kr/$3,640/£1,820).