For a good half-day trip outside of Annecy, check out the Gorges du Fier. Here you can experience the natural beauty of the gorge on a pathway literally anchored to the sheer rock face about 88 ft/27 m above the Fier river below. It's not a long walk through the gorge itself, only about 0.5 km round trip, but once you exit the gorge there's an open area next to a larger river that makes a good rest/swimming spot.
Open: March 15 - October 15.
Cost: No more than 5 euro.
Bottom-line: Provides an interesting perspective of the precipitous gorge walls that you'll rarely find elsewhere. Highly recommended if you have the time and transportation.