Danzturm, Observation tower in Iserlohn, Germany.

The Danzturm is a 28-metre observation tower on the Fröndenberg above the Rupenteich, built in 1908/1909 directly against the extension buildings of the former optical telegraph station No. 43. The slender tower of local rubble masonry with bossed corner quoins rises three storeys in the manner of a bergfried. A viewing balcony on brackets runs along the north-east, south-east and south-west sides, reached by a north-west stairwell with 100 steps. The restaurant is in the neighbouring building, not in the tower.

The Danzturm was built in 1908/1909 directly adjoining the extension buildings of the former optical telegraph station No. 43, part of the Berlin–Coblenz line established in 1833. It is named after Ernst Danz (1822–1905), an honorary citizen of Iserlohn who died on 28 May 1905. A folk festival and bazaar in the Alte Halle on the Alexanderhöhe on 10 and 11 October 1908 raised about 12,500 marks for the construction. The tower was inaugurated on 22 May 1909 and listed as a monument on 5 January 1987.

The tower is named after Ernst Danz (1822–1905), an honorary citizen of Iserlohn and a founding member of the Sauerländischer Gebirgsverein, which placed a memorial plaque reading "Zum Andenken an Professor Ernst Danz 1822 – 1905" on it. From 1957 to 1975 the association published a local-history journal also called "Der Danzturm". Until the 1970s the Iserlohn brewery used the tower on bottles, glasses and lids, and it remained in the company logo until the brewery closed in 2014.

Access is available and free during the restaurant's operating hours. Visitors climb about 100 steps to reach the viewing platform at the top.

The tower was built directly onto the extension buildings of optical telegraph station No. 43, part of the Berlin–Coblenz line set up in 1833. A plaque on the tower commemorates Professor Ernst Danz (1822–1905), a founding member of the Sauerländischer Gebirgsverein. From 1957 to 1975 the association published a local history journal also named "Der Danzturm".