"Castles in the Sky" is a song by Belgian music project Ian Van Dahl from their debut album, Ace (2002). The vocalist is Belgian singer Marsha, who also co-wrote the song.^[1] The single was released in Europe in 2000 and the United Kingdom in 2001. The song was a modest success in mainland Europe and was a hit in the United Kingdom, peaking at number three on the UK Singles Chart and number one on the Scottish Singles Chart for two weeks.

Belgian singer-songwriter Martine D. J. Theeuwen, better known as Marsha, heard that brothers and musicians Erik and Geert Vanspauwen were looking for a vocalist with experience in dance music. After getting in touch, Marsha had a successful audition and began working with the brothers until Geert "felt he was no longer needed" and quit, leaving just Erik and Marsha. About a year later, Christophe Chantzis joined the team and Marsha was given a demo that would ultimately become "Castles in the Sky". According to Marsha, A&S recordings took the song to the Midem festival and the song was subsequently "signed for eight countries." Though Vanspauwen and Chantzis are credited as co-writers of the song along with Marsha, she claimed: "The vocal melody and the lyrics of 'Castles in the Sky' are mine. No co-writers, the lyrics were taken as I wrote them." She went on to note that Chantzis "hated" the lyrics and the vocals, leading him to produce the Absolom remix without any vocals.^[1]

Controversially, however, Marsha was axed from any live performances, as three dancers (including Cindy Mertens) took her place.^[1] Later, Mertens and the dancers were also dropped, and Annemie Coenen became the frontwoman for the group. While initially lipsyncing to Marsha's vocals in live performances as well, a version of the song with Coenen's vocals was eventually released on the album Ace.^{[citation needed]}

There are two different videos for the song, both of which feature Cindy Mertens miming to Marsha's vocals. The first uses the regular radio edit, and shows a selection of dancers in an underground sewer. The second video uses the Peter Luts radio edit and features clips of an instrument being played amongst clips of the original video.