These Great Lakes sea caves accessible by boat in the summer turn into temples of ice reachable by foot in the winter.

Eons ago, a rushing lava river formed this pristine passage through solid rock.

This woodland architectural installation acts as a camera obscura for the heavens.

This futuristically sylvan church is a glass-enclosed marvel of modern architecture.

Giant, natural amphitheaters made of delicate geological formations called "hoodoos."

A common entry point to the Griffith Observatory trail holds its own wonders.

One of the most scenic stretches of road in America winds between some of the country's oldest trees.

The scuba diving training facility was named for the steam that rises from the cave's chimney.

The eerie remnants of an ancient forest were hidden under the sand for centuries.

Rare recess caves fill this unbelievably beautiful Ohio park.

More gold than anywhere else, ever.

This maze-like slot canyon is a unique gem within an already fascinating geological area.

Hundreds of glow-in-the-dark objects light up a museum in a historic zinc mine.

The largest hot spring in the United States is, as the name suggests, a stunning show of natural color.

A whimsical village of unique treehouses resides in a Washington forest.

A stunning, two-tiered waterfall made famous by poets, artists and the legend of a ghost dog.

This natural wonder drops 16 stories straight down through rare flora and streaming waterfalls.

Hollowed out cedar log tubs set in an ancient towering forest.

Towering basalt columns, a creation of fire and ice.

Wild lights and sound effects turn a walk through some caves into an eye-popping 1960s tourist attraction.

The longest continuous lava tube in the continental U.S. offers 2.5 miles of dark explorations for the adventurous.

Scores of vintage street lamps shine along L.A.’s Miracle Mile.

This semi-secret garden in south Seattle emulates a traditional Japanese garden using the plants of the Pacific Northwest.

A modernist landscape of water and sci-fi concrete.