Oak of Bad Blumau, Natural monument in Bad Blumau, Austria.

The Oak of Bad Blumau is a protected natural monument standing in the municipality of Bad Blumau, in the Styria region of Austria, reaching about 100 feet (30 meters) tall. Its trunk is exceptionally wide and its broad crown covers a large area of the surrounding forest floor.

A lightning strike in the 1970s caused serious damage to the tree, after which the hollow trunk was filled with concrete in an attempt to stabilize it. That repair work later turned out to create drainage issues that affected the tree from the inside.

Locals call this oak "dicke Oachn", a dialect expression meaning "fat oak", which shows how familiar and close this tree feels to the people of Bad Blumau. It has long been a reference point in the village, something people point out to visitors as a natural landmark worth seeing.

The oak can be reached by following the Bad Blumau circular hiking trail 3 or the FF8 bicycle path, both of which pass through the area. Sturdy footwear is a good idea, as the ground around the tree can be uneven.

Seven adults are needed to encircle the trunk, which measures 8.75 metres around and 2.50 metres across. The tree was once a meeting and dancing place for the community. A white-and-red shield marker is fixed to the fissured bark at the base.