An artsy hidden staircase leads to breathtaking views of San Francisco.

A pair of slides and a tree-lined stair corridor have been an urban oasis for nearly 40 years.

Spanning an elevation of 160 feet and containing 388 steps, this is Seattle's longest staircase.

Stairs often replace streets on the steep slopes of this old mining town.

Bring your own cardboard to the slippery slopes of concrete hidden in a neighborhood park.

A small flooded ghost town with a few scattered structures remaining.

A luxuriant botanical garden below sea level.

Remants of foundations, streets, and streetcar tracks inhabit the cliffs where a landslide occurred in 1929.

Nature took her revenge on the "Wickedest City in the World."

A mysterious monument meant to be a guide into "an Age of Reason" was destroyed after an apparent bombing.

A small museum filled with over 1,000 clocks, and one particular clock calibrated to run until the year 9999.

Native Americans built this circle of stones, which was used to predict astronomical events.

The longest living non-clonal organisms on Earth.

Natural catch-basin rocks covered in thousands of drawings spanning many millennia.

A perfect circle of twenty-four mysterious holes dates back to prehistoric time.

The ancient tomb acts as a calendar that keeps perfect time.

The largest earthwork effigy in the world.

A time-capsule monument reminding future generations of the importance of efficient and effective use of natural resources.

An ancient capital city that dates back 3,000 years old and harbors many surprises.

Living fossils in this remote Australian bay provide a glimpse of what Earth may have looked like 3.5 billion years ago.

Four bald cypress trees in Lafayette Square, across from the White House, mark the southern edge of a 100,000 year old cypress swamp.