Spiez Castle (German: Schloss Spiez) is a castle in the municipality of Spiez of the Swiss canton of Bern. It is a Swiss heritage site of national significance.
The massive square keep was built around 1200. The lower walls are about 3 m (9.8 ft) thick though they become thinner higher up. At the bottom it is 11.3 m × 11.2 m (37 ft × 37 ft). The tower increased in height several times over the following centuries before the final construction phase in 1600. In this final phase the tower was raised and crowned with hipped roof that brought its total height to 39 meters (128 ft). The keep was originally surrounded by several free standing wooden buildings. Over the following centuries these buildings were replaced with a stone curtain wall and a ring of two concentric ditches.
A gatehouse was built adjacent to the keep, which opened toward the west. Around 1300 a residence wing was added north of the keep. It was probably lower at that time than it is today and was connected to the keep by a wooden gallery. During the second half of the 13th century a number of tournaments must have been held around the castle because the visiting knights carved graffiti into the plaster of the main chimney. In the 14th century an additional north wing was added onto the residence wing. From the 15th to the 18th century, the castle was gradually renovated to its present appearance. The gallery was expanded and another story was added to the residence hall. The Trüel was added to the north-west side of the keep in the 16th century. Then, in the 17th and 18th centuries, the Baroque "New Castle" was built on the south side of the gatehouse.