Try summiting one of Southeast Alaska's 16,000-foot peaks and you'll run into a few potholes—literally. Thousands of pits (or moulins), up to 300 feet deep, scar 3.2 million glaciated acres of Wrangell–St. Elias National Park and Preserve, and more and more visitors are trading in a summit bid to rappel down one of the frozen gorges. Last July, I hooked up with St. Elias Alpine Guides to try out "moulineering." Equipped with ice axes and crampons, I was belayed into the mouth of Big Mama, a 150-foot-deep cavity leading to otherworldly caves and passages. Inside, eerily lit ice sculptures radiated various shades of blue as a waterfall crashed down the chamber's shaft, forming giant pools below. Before descending, I'd reviewed ice-climbing techniques and knots with the SEAG crew, so I was comfortable enough to plunge 100 feet into the cave (some moulineers are known to drop all the way down and scuba-dive the icy depths) before digging my crampons in, climbing from the abyss, and heading back to the wood-fired sauna reserved for customers on SEAG's multi-day trips. Full-day lesson, $350; full-day group lesson (up to six), $120; steliasguides.com; doubles at Kennicott Glacier Lodge from $295, including meals; kennicottlodge.com.