The 13th Floor is the fourth full-length album by the Norwegiangothic metal band Sirenia and their first with the Spanish vocalist Ailyn. It was released on 23 January 2009, through Nuclear Blast. The album features guest appearances by Jan Kenneth Barkved (who had also made some guest appearances on their album At Sixes and Sevens), and the French violin player, Stephanie Valentin, who adds to the sound along with the choir that has been a part of their sound since the beginning. The album was released in three formats: CD, CD-Digi and box set. The box set edition was restricted to 500 copies worldwide. The download-only single, "The Path to Decay", was released on 26 December 2008.