Set into the natural rock behind a small metal gate in the town of Pittenweem, United Kingdom, St. Fillian's Cave is thought to have been the dark cave where the titular holy man composed his writings by the light of his glowing arm.

According to legend, a 7th century Irish missionary named St. Fillan hid out in this small cave as he tried to convert the local Picts to Christianity. However, the cave was so dark that he realized he couldn't read his scriptures or prepare his sermons. When he asked God what to do about this problem, God gave St. Fillan a magical glowing left arm. So now Fillan could happily read and write with his right arm, while lighting the pages with his glowing left.

Whether any part of the story is true, in the following centuries, the cave was used as a part of a nearby monastery, as a smuggler's den, and as a prison during the witch hunts of the 17-18th centuries. The cave branches off into two prongs, one ending in a blocked staircase that once led up to a chapel garden. 

Currently one can visit the cave by picking up a key for it's iron gate entry at the nearby Pittenweem Chocolate Cafe. The key costs £1 though that may be per person.