The Highline is considered one of the quintessential Glacier NP experiences, and for good reason. It's not an incredibly strenuous trail (unless you add the Grinnell Overlook spur, which I highly recommend for the full Highline effect), but the length is challenging.
Come prepared, this trail has the most medical rescues in the park. You need lots of water, bring some snacks, good shoes and sun protection.
In order to complete this trail point-to-point you'll likely be out there for 6-8 hours. There are places to rest, hike to Granet Park Chalet for one of those breaks.
This was the grand finale of our week in glacier and probably the best way to end a vacation.