An emerald-green grotto just a short trip from Austin.

An exquisite tunnel of cascading flowers.

The United States’s oldest funicular railway glides up and down a steep Pittsburgh street.

Frank Lloyd Wright's most iconic home dangles over a Pennsylvania waterfall.

An easily overlooked memorial to a Ukrainian famine-genocide that killed over 4 million people.

The remains of Martha, the last known passenger pigeon, serve as a tool to educate about conservation.

People escaping slavery may have hidden inside a corpse vault.

Half of a waterfall goes into the river while the other half seems to disappear.

An unusually designed bridge from the 1920s was built to withstand the tides and winds of Maine.

A chance to sleep among the firs and pines of the Oregon forest.

A vertically floating hemlock controls the waves and weather at Crater Lake.

The world's smallest park was dedicated in 1948 as the only colony for leprechauns west of Ireland.

Only known mainland rookery of the threatened Stellar sea lion.

The second largest waterfall by volume in the U.S., Willamette Falls is outdone only by Niagara in the amount of water that is pushed northward.

This lake in the Cascades lives up to its name, disappearing down a hole every spring.

Treehouse motel and treehouse-building school.

According to folklore, Vermont's slanted windows were installed to keep witches from flying into the house.

The Vermont square that inspired Shirley Jackson's "The Lottery."

Stand at the center of this lakefront sundial, and you'll become part of the timepiece.

Cryptid lake monster honored with its own monument.

An elaborate Mayan city shrouded in alien conspiracy revealed the tomb of Pacal the Great.

No telescopes, no power, no gift shop: The Observatory of Chichen Itza, one of the world's oldest observatories, takes astronomy back to basics.

Every equinox this Maya pyramid puts on a spooky ancient light show.

Narrowest house in Boston.