The Cascade Canyon hike is near perfect. You can take a shuttle boat across Jenny Lake to get to the trailhead, which we highly recommend. All the difficult part is at the beginning of the trail. First you come to Hidden Falls.
Next comes a stretch that’s steep, rocky, and narrow. It’s the most difficult part.
Beyond that is Inspiration Point, a wide, flat area with a great view across the lake.
After that, it’s mostly level going back into the canyon, so if you make it that far you’re good. There’s varied scenery along the trail, so it doesn’t get boring: open, canyon, woods, and a stream nearby.
There were enough people to feel secure yet not crowded. We hiked back 2:45 and back out in 2:30, with stops to watch moose en route. We also saw partridge-like birds, a western tanager, and a pika. And heard lots of pika! Here’s one of the shuttle boats. It is a little odd when lots of people get off the boat and start hiking as a crowd but it thins out as people find their pace.