Red Rock Canyon is the perfect way to burn off all the calories you consume while in Vegas. It is a short ride from downtown and offers amazing views of the city. There is a small fee to enter the park (per car). Be sure to first go to the Visitor's Center and look at the exhibits. The workers are knowledgable and will be able to recommend a hike/walk for your activity level. They also have maps for you to use. If you are not in the mood (or shape) for a hike, there are easy walking trails and even a scenic drive around the canyon.