How does a Midwesterner say aloha?Nowadays, many heartlanders are skipping their winter escape to Hawaii or the Caribbean and checking in instead at the region's 71—count 'em, 71!—indoor water parks, 15 of which have opened this year alone. Inside these Biosphere-like enclosed summery settings, the air is eternally 80 degrees, and there's a slide, a ride, and a swimming pool for every age group, plus lounge chairs and margaritas for Mom and Dad. The best parks have adjoining hotels and are open only to guests. Two such chains, Kalahari (www.kalahariresort.com) and Great Wolf Lodge (www.greatwolflodge.com), have splashy outposts in Wisconsin, Ohio, Kansas, and Michigan. Ski resorts are catching the wave, too: at Boyne Mountain in northern Michigan, the four-month-old Avalanche Bay (www.avalanchebay.com) is equipped with a water-basketball court and tubing river. Spend your next snow day in a bathing suit! —E.S.