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).
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.