Johnston Canyon is one of the most popular hikes in Banff - it has an easy terrain, only takes about 2-3 hours, and has really amazing views from trails along and platforms directly above the canyon. Head out in the early morning or later into the afternoon to large avoid crowds.
Johnston Canyon is about 30 minutes outside of Banff, there are signs on the highway and along the way that make it really easy to find. There is also a small hotel/resort with a gift shop, cafe, and ice cream stand at the entrance of the trail. In the summer prepare for a lot of people and a very full parking lot. Just park on the road and walk to the trail instead of trying to navigate the packed lots.
The hike consists of a Lower and Upper falls. The lower falls have a really incredible viewing area that allow you to walk through a small cave/walk way in the rock and out onto a small gated area directly across from the falls.
The hike to the Upper Falls gets slightly less crowded as the trail opens up with a lot of different viewing areas and benches to hang out on. You'll also walk by some off the path trails that lead down to the river and give you better views of the canyon and waterfalls. Some trails seem safer than others, but a lot of people explore off the main path and I've never heard of anyone having issues or getting into trouble.
Most people only hike the 2-3 hour it takes to view the Lower and Upper falls but there is a longer hike that extends past the Upper Falls called the Ink Pot trail which we highly recommend! Check back in a few days to see our photos from the Ink Pots.