A former convent for Cistercian nuns, the 14th century Sankt Burchardi Church is home to one amazing musical instrument.

The automatic organ tucked away in the church is in the process of playing John Cage’s “As Slow As Possible,” a piece of music that will last for 639 years if played continuously. Started on September 5, 2001, the piece is expected to finish in the year 2640.

Cage wrote the piece back in 1985, but with no indication of how long it was meant to last. Some organists became interested in how it could connect to the lifespan of the instrument, which for an organ with its changing parts can be infinite, and the idea was put into practice in Halberstadt.  Comprised of just six pipes, the organ at Sankt Burchardi was built specifically for this piece of music, and is constantly maintained while it continues to produce notes. In fact, it wasn’t even completed until 2009.

“As Slow As Possible” opened with 17 months of silence. So though it started at the Sankt Burchardi in September of 2001, the first note wasn’t heard until February of 2003. Individual chords last for several months or years, with weights being shifted to different pedals when a new chord is called for in the score.