This is the legend surrounding the beginnings of Out Stack...
Herma and Saxa were giants: they quarrelled as they fell in love with a mermaid singing on the Flugga rock, throwing stones at each other which landed in the sea to become Saxa’s Baa. A large one thrown by Saxa became the Out Stack. To be rid of them she agreed to marry whichever would go with her to the North Pole. Both followed and were drowned as they could not swim.
In another version a passing witch settled the dispute by shrouding Saxa in turf to form the hill and turning Herma into a wreath of mist over the ness.
...taken from the Shetland Today website