KILAUEA VOLCANO, HAWAII
Welcome to winter's hottest vacation destination—on Hawaii's volcanically active Big Island. Glowing lava from Kilauea's flank can top 2,000°F. The volcano typically spews enough molten rock every day to pave a 20-mile-long two-lane road. But eruptions can slow, stop, or shift direction at any time. It all depends on Pele, goddess of fire, who lives in the crater. "It's just one of those things," says park ranger Mardie Lane. "Are you feeling lucky?" Sometimes—not always—you can see the lava flow from a viewing station just outside Hawaii Volcanoes National Park, a 1.5-mile hike beyond the south end of Highway 130. Come at dusk to see incandescent crimsons, yellows, and oranges. (808) 985-6000, nps.gov/havo or lavainfo.us.

APE CAVE, WASH.
Inside Ape Cave, a 13,042-foot lava-walled tunnel near Mount St. Helens in Washington, look for the Meatball (a suspended boulder) and Railroad Tracks (parallel lava ridges). Or tackle the cave's eight-foot lava fall.
(360) 891-5000, fs.fed.us/gpnf/recreation/ape-cave.

LAVA BEDS N.M., CALIF.
Explore dozens of accessible caves at Lava Beds National Monument in northeastern California. Most are open year-round. To see ice formations, traverse a slippery slope into Crystal Ice Cave on a ranger-led winter tour. (530) 667-8100, nps.gov/labe.