Mysterious 500-year-old tapestries depict a unicorn hunt.

The most confusing clock in New York.

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

Hear the quietest sound from across the dome.

Ride the subways of yesteryear.

San Francisco's urban bison herd has persisted in the face of extinction, development, and disease.

Lie in a hammock where George Washington stood.

Visit the monolithic tomb of America's most famous general.

Explore the largest pure gypsum deposit in the world, and go dune sledding while you're at it.

This sculpture by artist Fritz Keonig survived the 9/11 attacks and now stands as a monument to the victims.

A curious fountain that has no water and includes Satan, a crab, and 9 giraffes.

Elevated freight railway turned wildly successful urban park.

A museum dedicated to the alleged Roswell Incident.

A modern zoetrope on the New York City subway.

Twenty-seven massive radio antennas on the high plains of New Mexico search for life on other planets.

The crown jewel of the Queens Museum is a nearly 10,000-square-foot architectural model of the city originally built for the 1964 World's Fair.

A crumbling hospital from the 1850s on Roosevelt Island.

The most visited, and possibly most controversial, museum in Germany.

An artist's cute bronze subway sculptures belie his violent artistic past.

This exemplar of modernist architecture is meant to captivate and inspire students of the Cooper Union.

Whisper secrets in a busy station only to be heard on the other side of this acoustic arch.

The second-largest cave chamber in the world was discovered in 1898 by a 16-year-old and a friend known as "Pothead."

A collection of 20th-century automata, penny arcade games, and musical contraptions.

The remnants of two World's Fairs are here, complete with a 12-story globe, a mini-Manhattan, and a UFO-shaped pavilion.