Hidden in Central Park's Ramble is a troublesome cave buried just beneath the surface.

This theater opened in 1998, but both the building and the puppeteers who perform there have a distinguished history.

Climb right into the heart of this colorful Iceland volcano.

A geothermal paradise with bubbling mud pools and bright blue hot springs.

This eye-popping Icelandic crater lake is surrounded by red volcanic rock.

This valley of hot springs and boiling mud pots is home to the record-holding "Geysir," which originated the English word.

Every summer local children form "pysja patrols" to save young birds that have wandered from their nests.

This fantastical waterfall is hidden in a cave located in a cracked cliff.

This replica Viking village was created for a film that was never shot and is now open to visitors.

The most powerful waterfall in all of Europe.

This elegant arc of a waterfall marks a religious turning point.

The oldest church in Iceland is one of the few to feature ornate decoration.

This museum dedicated to divination also honors a local 10th-century prophetess.

Rising from the sea like a stone monster.

America's oldest Eastern European synagogue provided the immigrants of crowded Lower East Side tenements a space of sanctuary.

Built as a gift to the hottest tastemaker of the time, these hidden quarters remain an Art Deco showpiece.

Amid the marketing blitz of modern Times Square is an elegant holdover from its showbiz glory days.

A Victorian natural history and ethnographic museum with wonderful turn-of-the-century, science-book-esque evolution displays.

An exhibit of endangered species confiscated from smugglers and passengers.

Amid the bustle and noise of the Financial District hides a secluded garden oasis above the city streets.

This mosaic dedicated to John Lennon was tended for years by a Beatles super-fan.

A treasure trove of artifacts, books, and artwork from the "golden age" of exploration.

Everyone from Mark Twain to Teddy Roosevelt has a pipe hanging from the walls of this historic chophouse.

This study room in the New York Public Library saw the creation of one of contemporary America's greatest traitors.