The world's longest known cave system.

The first declared National Monument in the United States.

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

Once strictly off-limits, this lower level housing curious and priceless vehicles of the Petersen Automotive Museum is now open to the public.

A prohibition-style speakeasy takes up residence in the last Victorian residence in Hollywood.

This geothermal hot spring hides beneath a slowly growing mineral dome.

This abandoned Navy base was transformed into an off-grid alternative living community for thousands of people.

Few other hotels can rival the grandeur of the Castle in the Rockies.

This prehistoric sinkhole lured exclusively male mammoths to their death, much to the delight of science.

The granddaddy of all tourist traps, built on ice water, jackalopes, and a giant dinosaur.

143 feet of leaping muskie whose mouth can be used as a wedding venue.

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

The king of U.S. high points towers over every other peak on the continent.

The watery grave of an impractical idea.

This rare vessel mixed luxury with labor before being converted to a museum and sometimes haunted maze.

Duluth mineral magnates built this charming art deco lodge to be their private clubhouse.

This posh mansion began as a family's estate and ended as the site of a murder ripped from the pages of a pulp novel.

This picturesque cliffside beacon no longer calls to sailors but shines once a year in honor of a famous shipwreck.

The only arched bridge made of stone on the entire Mississippi River.

At this Minnesota state park you can easily wade across the source of the mighty Mississippi.

Secret hideaway for an alternative beach experience.

When flour explodes, it's not a pretty sight.

A toweringly silly piece of modern art has been delighting locals since the 1980s.

Home to the Amorphophallus titanum "Corpse Flower," which is among the largest flowers in the world and also smells powerfully of rotting flesh when in bloom.