Schloss Mühlegg, building in Gössendorf, Austria

Schloss Mühlegg is a two-storey castle with a hook-shaped ground plan, built in the 17th century, in Gössendorf about 8 km south of Graz. Its plain facades carry several coats of arms and memorial stones. On the courtyard side of the upper floor runs a two-storey arcade with basket-arch arches, partly walled up and glazed in recent times.

A mill was first recorded on this site in 1355, giving the estate its name; the estate belonged to the Graz Hubamt until miller Jobst Müller acquired it in 1575. Johannes Kepler married Müller's twice-widowed daughter Barbara in 1597 and lived in the house until 1599, when his Protestant faith forced him to leave the country. Michael Müller added "von und zu Mühleck" to his name in 1603 and was later raised to hereditary knighthood.

The name Mühlegg, also written Mühleck, comes from the mill first recorded on the site in 1355. In 1603 the miller Michael Müller added "von und zu Mühleck" to his name and was later raised to hereditary knighthood, so the miller's family name became the estate's name.

Schloss Mühlegg stands at Schloßweg 2 and 4 in Gössendorf, about 8 km south of Graz in the Mur floodplain. Since 1974 the Styrian Chamber of Commerce has run it as an apprentice dormitory, with new buildings added around the old house, so the grounds are not open to visitors. The site can be viewed from the public road.

An astronomical tower was originally built on the grounds for famous astronomer Johannes Kepler but was demolished in 1868. The roof structure of the castle still shows traces of where this tower once stood.