The trail is described in detail in various books and websites related to Glacier National Park; this report deals with my impression of the trail.
The trail to Hidden Lake begins behind the Visitor Center at Logan Pass. A large portion of this hike is on a boardwalk BUT the boardwalk does not mean it is for wheelchairs - you MUST stay on the boardwalk because it is there to protect the ground from humans! At a certain point, the boardwalk ends and the trail is hard packed dirt. The vast majority of the trail goes uphill, not at a steep angle but at an angle you'll feel in your legs and possibly your lungs due to the higher altitude.
This was one of the "greener" parts of the park we saw and one of the most crowded with hikers. There are numerous small waterfalls and wide open vistas to photograph or just enjoy with your eyes. This hike is one that you should plan to traverse at a leisurely pace - enjoy the scenery as you go toward the end of the trail at the viewpoint which gives you a very good view of Hidden Lake. There is a trail leading down to the lake from the viewpoint but we didn't take it.