Park naturalists lead several different hikes each day in Many Glacier Valley [1]. Hikers with a modicum of stamina and a passing interest in geology should try to catch the naturalist-led hike to Grinnell Glacier. In combination with a boat shuttle across Swiftcurrent and Josephine Lakes ($18), the all-day hike is eight miles round-trip with a 1,600-foot elevation gain. (Forgo the boat rides and it becomes 11 miles.) Grinnell Glacier reached its peak size during a sort of miniature ice age in the 1800s. Melting since then has left two smaller glaciers: The Salamander clings high on the Garden Wall; Grinnell Glacier proper is below and to the left. A warming trend starting in the 1980s has enlarged the iceberg-laden lake beneath the glacier, making it particularly hazardous to walk onto the glacial ice.
Watch out for bears on the trail to Iceberg Lake, an aptly named glacial lake 4.7 miles from the trailhead in the Swiftcurrent parking lot. The trail crosses alpine meadows before dropping into a cirque holding the milky blue lake. Mountain goats, marmots, and an occasional bear share this path with myriad hikers.
Take the same initial stretch of trail to reach Ptarmigan Falls (two miles) and Ptarmigan Lake (4.3 miles). The waterfalls and flower-strewn meadows make up for the steepness of the trail. Hikers reaching the lake with boundless energy should go another mile to the 183-foot-long Ptarmigan Tunnel, which emerges onto the north face of the Ptarmigan Wall, looking out to the Belly River country.
Links:
[1] http://www.moon.com/destinations/montana/glacier-national-park/many-glacier