Perhaps the coolest summer activity on the mountain is the three-hour Walk in the Treetops (406/862-2900, 9:30 a.m. and 1 p.m. daily, some 5 p.m. tours late June–early Sept., $54, reservations required), which starts with a shuttle or one-mile bike ride, then segues into a naturalist-led hike through the forest canopy on a boardwalk suspended up to 60 feet above the ground. Though walking across a fairly narrow plank suspended far above ground sounds like some terrifying character-building exercise, the solid cable-rigged railings and the securely tied safety harness on each participant make this adventure accessible to all but the most acrophobic. After a few minutes of getting used to the height, the treetops begin to seem like a great place to view not only the nearby lakes and mountains, but a wide variety of bird life, such as western tanagers, red tail and kestrel hawks, pine grosbeaks, and kinglets. Squirrels, pine martins, moose, deer, and coyotes may also be spotted. Participants must be at least 10 years old and 54 inches tall.