Height: 4,882 feet/1,488 meters Best For: Volcanologists, devils Hekla is Iceland's second most active volcano. With eruptions recorded far back into prehistory, it last blew its top in February 2000—but that doesn't mean hikers can't scale the famed stratovolcano. You may want to do it soon, however, since Hekla rarely lays dormant for long, and reports of magma buildups have some scientists claiming that an eruption is due. When this peak does erupt it gives very little time to escape: There was a mere half hour warning before the 2000 event. But it's worth it for the opportunity to stand atop the long ridge that makes up one of Earth's most temperamental spots, the view stretching out across a landscape built from much of the tephra that spewed from the steaming hot spots surrounding you. The Hike: The trail to the top crosses snowfields, and it's a fairly easy three- to four-hour hike (though it may be wise to carry glacier gear or even skis). It's so easy, in fact, that some choose to snowmobile up it in winter. Hekla lies just 44 miles from Reykjavík, and outfitters like Icelandic Mountain Guides pick up hikers at their hotels for a day trip to the top (and keep tabs on seismic activity so you're not there when the peak blows up). At the Top: There's a certain allure to hiking on the Gate to Hell, which is exactly what medieval churchmen claimed Hekla to be after its first recorded eruption in 1104. That's understandable, since the volcano spews an inferno of tephra bombs, ash, and lava when it bursts.