These ruins are all that remain of what a Spanish barrack that likely housed a quarry overseer, masons, and stone cutters involved in the construction of the Castillo de San Marco.

The highest point in Indiana is curated by an Eagle scout but may be in danger of losing its record to a nearby garbage pile.

The only freestanding table rock formation east of the Mississippi.

The longest navigable underground river in the United States is home to countless blind and albino animals.

This replica of the Greek structure is in the heart of Nashville.

One-time winter retreats of prolific inventor Thomas Edison and his friend Henry Ford.

The smallest post office in the United States is no bigger than a broom closet.

Former utopian colony based on the belief that the universe exists in a hollow sphere.

The hotel where Martin Luther King Jr. was shot is now a museum dedicated to his work.

Home to drunken tower-climbing goats... seriously.

Walk the whole Mississippi River!

This Memphis recording studio launched the careers of Jerry Lee Lewis, Johnny Cash, and Elvis Presley.

The bad-ass ride of a soul legend, housed in one of the world's few soul museums.

This head-spinningly bizarre Depression-era art cave is wall-to-wall quartz and Jesus.

An 18th-century Spanish watchtower made entirely of seashell and concrete.