Schloss Greinburg, Medieval castle in Grein, Austria.

Greinburg stands on the granite Hohenstein rock above the Danube at Grein, built from 1488 as a four-towered castle with an added gate tower, a palas and a chapel. It is considered Austria's oldest residential castle and the first castle complex north of the Alps laid out on a single regular plan. Inside are the arcaded courtyard, the late-Gothic Diamond Vault, the Great Knights' Hall (30 m long, 16 m wide, 14 m high), the castle chapel with an early-Baroque Christmas altar and the Sala terrena, a hall covered entirely in pebble mosaic.

Construction began in 1488 under the Prüschenk brothers with permission from Emperor Friedrich III., establishing this as Austria's oldest residential castle. The structure evolved through subsequent decades with multiple renovations to meet the changing needs of its inhabitants.

The castle's name changed over time: first Stettenfels, from 1504 Heinrichsburg, and only since 1533 Greinburg. The Great Knights' Hall measures 30 by 16 metres and 14 metres high; the castle chapel holds an early Baroque Christmas altar. The shipping museum that occupied the Small Knights' Hall closed in autumn 2025.

The castle stands on the granite rock Hohenstein directly above the town of Grein on the Danube, so the approach is uphill from the town below. The showrooms, including the Great and Small Knights' Halls, the Diamond Vault, the Sala terrena and the arcaded courtyard, can be visited from May to October daily except Monday, and are reached on a guided tour. The complex is a stop on the Danube Cycle Path and the Donausteig trail.

One interior room displays wall patterns made entirely from Danube River pebbles arranged into geometric forms. The effect is enhanced by natural light filtering through windows and casting shadows across the textured surface.