There's no better way to realize you're out of shape, even if you thought you were pretty athletic, than to rock climb. In fact, you may be a little shocked on your first visit to Mission Cliffs, the city's only indoor climbing gym, by how much strength, stamina, and mental determination it takes to snake up the walls. But climbing can be addictive, and after your first hour -- your arms quivering, calves shaking, and fingers aching -- you'll be jonesing for one more ascent. Originally designed for hard-core enthusiasts to train off-season, Mission Cliffs offers curious beginners and practiced experts a place to meet like-minded hard-bodies addicted to adrenalin rushes and near-death experiences. Housed in a renovated warehouse, the facility boasts a 50-foot-high lead wall with top-roping and lead-climbing routes of all grades and levels, 14,000 square feet of climbing terrain, and a brand-new bouldering area. The center also has a state-of-the-art weight room, cardio equipment, locker rooms, showers, saunas, and a well-stocked pro shop hawking the latest in gear, clothing, and guidebooks. Friendly instructors teach basic skills and advanced techniques through lessons, clinics, and even supervised programs for kids. Day passes are $10 to $20; full evening packages are $30 for a belay safety class, equipment rental, and unlimited climbing.