UnderTow, Phoenix's first underground tiki bar, has had up to three-hour waits since it opened last week. That's partly because the space is less than 500 square feet and seats only about 25 people, but it's also because the concept is an experience unlike anything else in the Valley. "This is a completely immersive experience," said Jason Asher, director of craft spirits and mixology for Young’s Market. Asher, along with Sip Coffee & Beer Garage owner Travis Radevski; Barter & Shake owner Rich…