You've been warned!
OK then. You're still here? Good!
Normally, I equate mountain biking and trail running with a trip up to Durham Forest. There are acres and acres of trails to get lost on, it's wonderful.
But what about mid-week, when one has an hour to burn? What then?
Answer: Cullen Central Park and Heber Down Conservation Area!
Cullen Central Park

Left behind? A small series of trails suitable for everything from hiking to biking.
Click here for a map.
If you're on a bike, it's possible to follow the top yellow trail across the creek right to the end of the arrow... keep an eye out to the north, and you can connect to Heber Down (via the Group Camping area). The town eventually intends to make this link more official.
Heber Down
Heber Down is a conservation area in north Whitby. Trees, trails, creeks, a taste of nature right next to the town.
Click here for a map and brochure
There are many trails in the park, mostly unpaved and suitable for hiking, trail running, and mountain biking.
The only caveat - many dog owners treat this as an off-leash area, despite the signage clearly stating dogs must be leashed. Take appropriate precautions.
Urban (and Suburban) Trails
Having been through various portions of the Toronto area, I know this is not entirely unique... sometimes a chunk of nature is right under your nose, you just have to find it. It may take a bit of exploration and a few dead-ends, but that's part of the fun! Happy Urban Trailing.