A local prank turned town icon.

The sunken structure looks like the victim of a catastrophic flood.

Once a sewer culvert, this road tunnel now offers cyclists and pedestrians a subterranean stroll under the C&O Canal.

Internet rumors, often involving Icelandic singer Bjork, have abounded regarding this isolated outcrop of rock.

A museum dedicated to the history and art of staying clean.

This little valley along Highway 1 is engulfed by thousands of lilies during the spring season.

Dine on ceviche tacos in the sea at this floating restaurant only accessible by boat.

Indents in the pavement are all that remain from a grisly death machine in Paris.

An unusual slot canyon in the Aztec/Navajo Sandstone has a cross-section like an inverted old-fashioned keyhole.

A dark, narrow tunnel that leads to a charming lake and waterfall.

Loyal fans of one television's most famous painters still come to pay their respects.

There's a crumbling old mansion inside the Smithsonian National Zoo.

The first lookout in Yosemite.

After several weeks of radio silence, this abandoned oil tanker washed up on a remote beach in Liberia.

The best way to get a sneak peek at the movies.

A historic structure that once housed pigeons used by farmers to help fertilize farmland.

Once considered one of the country's finest motte and bailey castles.

The entire length of the border is marked by a 20-foot-wide slash through the trees.

The marker offers a rare chance to be in four U.S. states at once, though there's some controversy over its geographic accuracy.

A sinkhole and now a swimming hole, too, full of dazzling turquoise water.

This secluded aqua waterfall in the Grand Canyon is the perfect swimming hole, and the Havasupai tribe's fiercely protected natural wonder.

There's a mini version of Iguazu Falls hidden in the Balkans, and it's got a rope swing.

These azure waters were thought to lead to the Mayan Underworld.

This cavernous swimming spot doubles as a home to the largest known colony of bats in Central Asia.