Burg Marquartstein, Medieval castle in Marquartstein, Germany.

Burg Marquartstein stands at 575 m on a rock above the Tiroler Achen valley. The group on the wooded slope comprises a white church with a tall thin spire and arched windows, a large grey stone building with a steep dark roof, rows of small dormer windows and a round tower, and a second grey stone building with a square tower rising from its roofline.

Marquart von Marquartstein founded the castle in 1075; after his early death it passed through his widow Adelheid von Lechsgemünd to the Diepoldinger and then, via Uta's marriage to Engelbert II, to the Spanheimers. In 1259 Hartmann I von Werdenberg sold the county to Duke Heinrich XIII of Lower Bavaria, and Marquartstein remained a Bavarian Pflegamt seat until 1803. In 1857 Jemima Montgomery and Cajetan von Tautphoeus bought the decaying castle and had it renovated; from 1928 to 1958 it housed a Landschulheim.

The castle is private and cannot be visited, so its cultural life is tied to the people who owned it. The English-Irish writer Jemima Montgomery, who bought the decaying castle in 1857 with her husband Cajetan von Tautphoeus, is documented as having drawn inspiration for her novels here. The castle chapel next door, St. Bartholomäus and Vitus, was rebuilt after a fire on 13 February 1843; there Richard Strauss married Pauline de Ahna on 10 September 1894.

The castle is privately owned and cannot be visited, so there is no interior access; the buildings stand on a rock above the Tiroler Achen valley and are seen from outside. The associated chapel of St. Bartholomew and Vitus stands beside the castle. Marquartstein can be reached by train on the Traunstein–Ruhpolding line.

The castle chapel beside the main buildings, dedicated to St Bartholomew and St Vitus, burned on 13 February 1843 and was rebuilt two years later. In it, on 10 September 1894, the composer Richard Strauss married Pauline de Ahna. The castle itself is privately owned and cannot be visited.