Once thought to date from around 1390, it is now believed that the world's oldest playable organ was constructed during the 1430s. The origins of this instrument are unclear, but it is known that the Freiburg painter Peter Maggenberg decorated the folding doors between 1434 and 1437. The cathedral-fortress itself, constructed during four periods over a span of 150 years, was completed in 1267.

Sebestyén has given recitals on this instrument several times during the course of his career, excerpts of which can be heard on the second LP published by the Festival International de l'Orgue ancien.