The best bet downtown is the Katy trail, a terrific 3.5 mile urban trail that runs between the American Airlines Center downtown and Southern Methodist University to the north, along the old Missouri-Kansas-Texas Railroad path. It is pleasantly shaded in spots and has good views of the Dallas skyline. It’s very popular, and there are lots of fun places to stop along the way.
You can add some variety by doing a loop incorporating some of the Turtle Creek trail and Turtle Creek Blvd. Cross points from the Katy Trail are Lemmon Ave., Blackburn Ave., Fitshugh, and Armstrong.
If you will be downtown, try to stay within a mile of the Katy Trail, which can be accessed from McKinney Ave. and the American Airlines Center at Victory Park.