Dallas
There's more places to run and bike than just White Rock Lake
When to come?: 

Dallas can be absolutely beautiful in the spring with the flowers and moderate temperatures, but gets extremely hot in the summer. Winters are constantly changing - it can be 70 one day and sleeting the next. Fall is usually nice weather, especially in November and December.

What to do if you have a sunny Saturday?: 

Do what everyone does to exercise in Dallas and head to White Rock Lake for running or bicycling. Heck, bring your dog and let him play in the off-leash dog park (fenced in) next to the trail.

Where can I go to get out away from the city, without driving too far?: 

Cedar Hill State Park is not too far from downtown, but you will get a little bit of the Hill Country. For piney woods and some great mountain biking, go a little further out to Tyler State Park.

You can also go to Fort Worth to explore their outdoor activities.

What are some great weekend getaways?: 

Dinosaur Valley State Park and the Granbury region southwest of Dallas is a great area to spend a weekend hiking, mountain biking, or relaxing by the lake.