This week, a diving enthusiast highlights the underwater world, from the turquoise coasts of Central America to the cold jade waters of Puget Sound. NPR's Steve Inskeep explains what Karachi, Pakistan showed him about the mega cities that are mushrooming around the world. Also, author Scott Wallace describes his trek deep into the Amazon and the quandary of trying to protect the fierce Arrow people from contact with the outside world. For more information on Travel with Rick Steves - including episode descriptions, program archives and related details - visit www.ricksteves.com.