Hidden in the northern region of Costa Rica, the Celeste River (Río Celeste) winds through Tenorio Volcano National Park with a color so vivid it seems unreal. The river’s striking turquoise hue is caused by a natural chemical reaction between two mineral-rich streams, Quebrada Agria and Río Buena Vista, which merge at a point known as "El Teñidero." This one-of-a-kind phenomenon creates the illusion that the water has been dyed blue, even though no pigments are present.

The city of Oporto is situated on the right bank of the River Douro, being the second largest city of the country. Oporto is the regional capital of the northern area.

Uyuni, in southwestern Bolivia, is best known as the gateway to the world’s largest salt flat, Salar de Uyuni. Once a humble railway town, Uyuni has grown into a base for travelers drawn to this surreal landscape, where an ancient dried-up lake has left behind a vast expanse of glistening salt crust.

Palm Beach, located on Aruba’s northwest coast, is the island’s most famous stretch of sand: a two-mile ribbon of soft white shore lined with turquoise waters and a lively resort scene.

Originating as a tiny fishing village in 1038, modern Kehl has become an important link between Germany and France. Rhine River cruises most often use Kehl as their gateway to the much larger and better-known Strasbourg. The savvy traveler, though, might choose to skip the jaunt across the river and enjoy many similar sights, shopping and cuisine as those offered in the teeming French city.