In the year 963, Count Siegfried, the founder of Luxembourg felt in love with Melusina, a pretty girl he met near the Alzette river.
She was a mermaid, a water nymph, able to show up in a human shape for 6 days in a row.
Siegfried asked her to marry him and she said: "I'll accept under the following conditions - I want to live in a castle on the Bock rock and want to spend the Saturdays alone."

Siegfried promised all this to her.
He realized that he didn't have enough money to build a castle and so he made a pact with the devil who proposed to make him a wealthy count if he'll sell his soul to him, which he would come to take 30 years later.
Siegfried agreed and over night, an impressive castle arised on the top of the Bock rock, which he named Lucilinburhuc.
He prepared a wonderful wedding and they lived in happiness for years.

One day, Siegfried got worried by the fact that his wife disappeared every Saturday and decided to have a look through the keyhole of Melusina's bathroom door.
He discovered that she was sitting in a water puddle, next to a well, combing her long hair. Instead of legs and belly she had a strange body and a fishtail.
He cried with horror and Melusina jumped into the well, which was leading to the Alzette river. Siegfried never saw her back in his life.

In 993, the deadline of fulfilling the devil's pact had arrived. Siegfried told his knights to protect all the doors and gates of the castle.
No chance, the devil came through a window, gripped Siegfried and both disappeared forever.

It is told that sometimes, Melusina is seen in the water of the Alzette with a golden key in her mouth.
Some say that she's hiding in a secret cave inside the Casemates, an underground tunnel system leading from the Bock rock to the Alzette river and through Luxembourg City.
There she's tailoring a linen dress for herself, one stitch every 7 years.
When her dress is ready, she will be able again to show up as a woman and the Bock rock will crumble down.