This year we got to 3 trails that often make the “best dayhikes in US National Parks list”: Grand Canyon’s Bright Angel Trail, Grand Teton’s Cascade Canyon Trail, and Glacier’s Highline Trail. The Highline continues further than we took it, but we did over 12 miles on the most popular section, completing the recommended dayhike route and then some.
From West Glacier, travel Going to the Sun Road up to Logan Pass. You can drive there, or (as we did) take free shuttle buses from the visitor center. The bus option requires a mid-trip vehicle change, from a large bus to a mini-bus that is more nimble in the twisty, switchback section of the Road. Go early to avoid lines, and try to sit on the right side for best views. It’s a spectacular ride, and the pass is great even if you don’t hike.

Logan Pass has an elevation of 6500 feet. It has a visitors’ center with bathrooms and rangers, and it’s the start for several long and short hikes. The Highline crosses the street and immediately becomes very narrow, with a steep drop-off to the left. There is a rail you can hold on your right, but a few people change their minds at this point, finding it just too scary. The narrow section is short, but the trail continually has a drop on one side.
On the left you follow the valley which opens up great views. Below you is Going to the Sun Road, and a steep U-shaped glacial valley. Tall waterfalls pour nearly straight down.

To your right, the slope continues up, forming a feature called the Garden Wall. The Wall is actually the northern Continental Divide. Water on the other side of it eventually flows into Hudson Bay in Canada.

The Highline goes slightly uphill (about 800 feet) for the first 3.5 miles until it reaches Haystack Butte. Some people turn around at this point, and they will certainly have seen a lot. Our route was point-to-point, making the shuttle bus necessary. After the Butte, the trail goes slightly downhill. It snakes around, exposing new views.

At just under 7 miles, there is a spur to the right that goes up to the top of the divide, to an overlook to Grinnell Glacier. I highly recommend this detour, which is about a mile in each direction and pretty steeply up. (After 7 miles of hiking on a hot day, we weren’t thrilled about this extra work, but the view is worth it.) The view straddles the continental divide.

Back down the Overlook trail, and then another mile gets to The Chalet. This is a few Swiss Alps style buildings where hikers can stay overnight, and a small expensive cafeteria. A lovely location.
The trail continues another dozen miles (eventually into Waterton Park in Canada), but we turn at this point, into the valley down a series of very long switchbacks that seem to go in the wrong direction. Eventually, they return to The Loop, a hairpin curve on Going to the Sun Road, and the site of a shuttle bus stop. We use the shuttle to return to West Glacier. Hikers who left cars at the Pass can take the shuttle back up. We have descended over 3000 feet. Definitely easier in this direction.