In the post-apocalyptic future, humankind will look to those who spent the most time at the gym for leadership, as they will be best prepared to combat the roaming packs of feral treadmills. Prepare for glory with today's Groupon: for $20, you get a two-month Black Card membership at Planet Fitness (up to an $89 value). This Groupon is valid at three San Francisco–area locations: Fremont, Hayward, and Daly City.

Planet Fitness' massive, brightly colored edifices teem with aerobic, strength-training, tanning, and massage options, tailored to suit burgeoning buffs of all ages and abilities. After an intense muscle pummeling on the extensive selection of strength-training equipment and free weights, valiant athletes and masochistic vampires alike may bask in the unlimited artificial sunshine of the gym's tanning booths. Meanwhile, shiatsu massage chairs stand at the ready, twiddling soothing robot thumbs and waiting to coax tension from tired tendons.

Planet Fitness' facilities also include full locker rooms, and gym members receive a Black Card key tag as well as a 50% discount on most beverages. Members may also bring a friend on any visit. Groupon users also receive a free startup if they sign up for a full Planet Fitness membership within two months of redeeming their Groupon, bequeathing wistfulness to formerly frequented couches.

Although Planet Fitness sometimes features a discounted price online, this Groupon still offers the best deal available.