#1 on that list: Mountain Biking! I have a Gary Fisher hybrid, an older one that leans more toward Mountain Bike than anything... so I slap some big fatty tires on it, and hit the trails. I like to get out in the fall and early spring, pretty much any time I'm not on the road bike training for a ride or race.
Durham Forest and the East Duffins Headwaters
Durham Forest is made up of several properties, totally over 1500 hectares of wilderness.
- The main Durham Forest tract
- The East Duffins Headwaters - Walkers Woods, Glen Major, North Walkers Woods, and the Brock Tract
Durham Forest is a good place for beginners. There are 4 very well marked loop trails that are well groomed and not technical. There are a few single-track sections that shoot off the main trail, but nothing too serious. This is probably the most popular section of the trails, you'll often encounter hikers, dogs, and other mountain bikers, so keep your eyes open!
Glen Major and Walkers Woods are located just south of the Durham Forest parking lot. The northern access point is on the west side of 7th concession, right next to the giant radar tower at the top of the hill (big tower with white ball at the top). There is another parking lot a few kilometers south of Chaulk Lake Road.
This is an enormous area with trails winding around everywhere. Lots of different terrain, from deciduous forest to pine trees to a recovered gravel pit... The trails are well marked with sign posts throughout, and each post has a tiny map on it so you can figure out where you need to be going. There's a bit more sand throughout this section (especially at the north end), and some of the single track can get a bit hairy. If that's not your thing, follow the "Trans Canada Trail" signs and it's fairly easy.
The Brock Tract is interesting, but I would leave it for last, once the others have been explored. It's not as well marked, and very few people are over there. There is a very cool pine forest on the far south side, though, that's worth the trip. Keep an eye out for hunters... in fact it's probably best to wear something very bright and not deer-like in any way...
I haven't been in North Walkers Woods yet, so I can't comment on it... it speaks to just how huge this area is, I've been there a dozen times and just can't get to everything!
Have fun! Be safe and smart.