Meet the cataphiles: Daniel Garnier-Moiroux crawls through a very tight section of the Paris catacombs. Stephen Alvarez/National Geographic hide caption

itoggle caption Stephen Alvarez/National Geographic

Steve Duncan, an urban explorer who has examined the hidden infrastructure of major cities all over the world, emerges from a manhole in New York City. Courtesy of Steve Duncan hide caption

itoggle caption Courtesy of Steve Duncan

Rocky Galloway (left) and Reginald Stanley, parents of twin girls, were married in Washington, D.C., on Tuesday. Jacquelyn Martin/AP hide caption

itoggle caption Jacquelyn Martin/AP

"What will God do when I die," Michael Geoghegan asked himself. "And I always thought — nothing." Jacki Lyden/NPR hide caption

itoggle caption Jacki Lyden/NPR

The historic steamship SS Lilac is docked at the River Project on the Hudson River. Students from New York's Harbor School made the trip to the river as part of their curriculum: The school teaches students everything from boat building and ocean ecology to oyster growing. Jacki Lyden/NPR hide caption

itoggle caption Jacki Lyden/NPR