The world's third-largest scale model of the planets.

The largest earthwork effigy in the world.

A castle built by an eccentric medieval enthusiast in rural Ohio.

Deep scars on the earth left by the Ice Age.

The largest ancient burial mound in Ohio.

A memorial for an outsider theorist who believed that the planet is actually hollow.

These sub-farmland caves are home to a majestic stalactite known as the "Crystal King."

The world's tallest doric column is this Ohio monument to a naval victory in the War of 1812.

An office built to look like a giant basket.

A favorite of Amelia Earhart, ranking among those rare bridges that can be crossed without changing sides of the river.