Underneath the ocean is a mirror image of the surface world, complete with upside-down trees, backward-moving escalators, and cities exclusively populated by doppelgangers sporting trimmed goatees. Steel nerves for submerged déjà vu with today's Groupon: for $20, you get one 60-minute Discover Scuba Diving experience from Surface Interval Scuba (a $50 value). Classes take place on Sundays at the Kirby Creek Natatorium in Grand Prairie, but Groupon purchasers need to visit Surface Interval Scuba’s store location in Arlington ahead of time to fill out a waiver and be sized for equipment.

Under the supervision of PADI-certified instructors, the one-hour course will provide water novices with the skills and confidence needed to embark on aquatic expeditions. Though the class won't churn out scuba divers certified to dive alone, it might finally put to rest a persistent fear of bathtubs and really big puddles.

Students will discover the mysterious workings of oxygen tanks and regulators, proper goggle-defogging techniques, and basic safety rules that apply to full-certification courses as well. Post-class, prepare to be able to shower for hours and retrieve all the coins from the bottom of a local fountain. Students who opt to continue onto open-water training will receive a 10% discount on gear purchases. Call ahead to schedule a class time.