Stables are scattered throughout Hyrule and are safe spaces for Link to rest or purchase equipment from Beedle. You can find the Gerudo Canyon Stable in the Wasteland Region of Hyrule. Kay Noh Shrine is direct to the south of this stable. If you speak to the owner of the stable, you can register your horse. That means if you ever need to visit the Gerudo Canyon Stable again, you'll have access to your horse.