Perhaps the most spectacular grotto along the Algarve coastline.

These wondrously illuminated caverns extend under the mountains of the Fukushima Prefecture.

This neolithic stone grave has been altered and restored so often its now more neo than lithic.

According to legend, this bell once belonged to a kingdom now lost beneath the waves.

A hidden tunnel leads to an abandoned slate quarry that's now a secret swimming spot guarded by cliffs.