The Don Valley, Toronto is a small valley located in central Toronto running from the Prince Edward Viaduct to Mount Pleasant Cemetery, Toronto, it also has a small river, the Don River runs down the middle ranging from one to two feet in depth in most parts. The ravine runs under a few bridges most notably the St. Clair bridge, as well as housing many different types of plants and animals it is also used for recreational purposes.
The ten kilometers of biking trails along the Don Valley are great for experts and beginners alike. The stretch of ravine between the Don Valley Brickworks up to Thornhill Park boasts some challenging trails, with exciting descents and climbs as well as some North Shore elements built in.
More information: http://en.wikipedia.org/wiki/The_Don_Valley,_Toronto