Iceland has some of the world's longest lava-tube caves, formed after volcanic eruptions when conduits of molten rock drain downhill. Lava pillars, mineral stalactites, ice candles, and snaking side passageways are among the intriguing formations within. Walking through these caves generally requires agility and sure-footedness but no specialized training or equipment, so virtuoso spelunkers tend to devote their energies elsewhere. Ice caves are also common in Iceland, but they're too dangerous to enter.
Among the many lava-tube caves worth seeking out are Raufarhólshellir, near Hveragerði in southwest Iceland; Surtshellir and Víðgelmir in west Iceland; and Lofthellir near Lake Mývatn.
If you plan to explore any caves on your own, bring a strong flashlight, warm clothing, and sturdy shoes. Helmets, knee pads, gloves, and headlamps are also advised, and caves with icy floors may require studded boots. The smartest procedure is always to seek out expert local advice beforehand.
Several Reykjavík companies offer caving tours, with all equipment provided. Arctic Adventures, Laugavegur 11 (tel. 562-7000; www.adventures.is), and Iceland Excursions, Höfðatún 12 (tel. 540-1313; www.icelandexcursions.is), offer 3- to 4-hour tours to Gjábakkahellir between Laugarvatn and Tþingvellir; Arctic Adventures leaves Fridays from June to August for 5,990kr ($96/£48), while Iceland Excursions leaves Saturdays and Sundays year-round for 6,400kr ($102/£51). Mountaineers of Iceland, Skútuvogur 12E (tel. 580-9900; www.mountaineers.is), leads 5-hour private caving tours by arrangement for 13,500kr ($216/£108), with a four-person minimum. Iceland Rovers (tel. 567-1720; www.icelandrovers.is) has a 6-hour tour that begins with caving and ends with a hike to the swimmable hot springs in Reyjkadalur. The cost is rather high at 17,900kr ($286/£143). Set departures are on Sundays, and private trips are on request with a four-person minimum.
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.