How low can you go? At this underwater watering hole, you can go about twenty feet down, to the sandy floor of the ocean. Think of it this way: Even if you hit rock bottom, you'll never again have to moan, "How dry I am!" Here you're as likely to see a mermaid as a barmaid. In a marketing stunt that sounds more like a drunken prank, tequila magnate José Cuervo celebrated the Mexican holiday Cinco de Mayo in 2000 by actually sinking a full-size bar, complete with six stools, about 200 yards off of the First Street beach on South Beach. But this $45,000 structure attracts more than potential consumers. Behind the bar a curved wall of interlocking tetrahedrons, made from recycled concrete by long-time artificial-reef builder Ben Mostkoff, promotes algae growth, promising sea creatures and divers a lush environment. So stick around for last call. Sometimes, round about 3:00 a.m., if you're really quiet, you can hear the shrimp sing: "José Cuervo, you are a friend of mine/I like to drink you with a little salt and lime."