A Dutch guide invites us to imagine a day on the water exploring Amsterdam's iconic canals. Then a historian shares what little we know of the elusive Sentinelese — likely the most isolated, least contacted people on earth — and what he learned by traveling to nearby islands in the Bay of Bengal. And a tour guide from Portugal tells us why the venerable university of town of Coimbra is such a delight to explore.

• Amsterdam-based tour guide Dennis Gerrits
• Adam Goodheart, author of "The Last Island: Discovery, Defiance, and the Most Elusive Tribe on Earth" (Godine)
• Lisbon-based tour guide Cristina Duarte

• Dennis Gerrits offers custom tours of Amsterdam and Holland.
• Rick takes a short cruise on the canals of Amsterdam.
• Adam Goodheart is director of the Starr Center for the study of the American Experience at Washington College, in Chestertown, on the eastern shore of Maryland.
• Adam is the author of "The Last Island: Discovery, Defiance, and the Most Elusive Tribe on Earth," published by Godine.
• Adam is included in the National Geographic film "The Mission," which explores the death of American John Chau on North Sentinel Island.
• Survival International advocates for protecting uncontacted tribes from outsiders. They discuss the John Chau death on North Sentinel Island on their website.
• The Rick Steves online guide to Coimbra, Portugal.
• Cristina Duarte's website includes information about her tour services.