Picture Lake is not technically in North Cascades National Park but the Mount Shuksan in the distance is. Getting here from the park requires a 2.5 hour drive.
Unlike some other trails, the views are pretty muted until the last quarter of a mile so this one really shouldn't be attempted until the snow to fully melts sometime in mid-late July.
The Hidden Lake Lookout Trail is one of the best hikes in all of the Pacific Northwest offering incredible views of staggering mountain peaks in all directions.