Annenturm, Althofen, Medieval fortified tower in Althofen, Austria.

Annenturm is a rectangular fortified tower built from quarry stone in Althofen, representing medieval defensive architecture with its solid construction. The structure features a ground-level rectangular doorway on the north side and a vaulted entrance positioned higher on the second floor.

In 1278 King Rudolf allowed Archbishop Friedrich II of Salzburg to fortify his market of Althofen; the work was carried out in 1307, when the market moved to the Upper Market and the Annenturm was probably built as an outwork. The tower lost its roof at least 300 years before 1957, when it received its present roof platform.

The tower takes its name from Anna Grobecker, a former owner. It is a protected monument (Denkmalgeschütztes Objekt) in Althofen and now serves as a television tower, with modern windows set into the old masonry.

The tower stands in the Oberer Markt of Althofen, with a high entrance on one side and two arrow slits each on two other sides. The 1957 roof platform is reached from inside; the masonry is about 2.5 metres thick. The topmost windows in the walls are modern additions.

The tower kept its roof for only part of its history: it lost it at least 300 years before 1957, when the present roof platform was added. The masonry, about 2.5 metres thick, was laid in low compartments, a technique first seen in Carinthia around 1260.