Achteckiges Haus, Cultural heritage monument in Darmstadt, Germany.

The Achteckhaus Darmstadt at Mauerstraße 17 is a two-storey, solid Renaissance building with an octagonal plan, a stair tower projecting to the west and a tent roof. It stands on a 16th-century square cellar with four groin vaults and a central column.

The octagonal garden house was probably built in the early 17th century by master builder Jakob Müller for Hessian chancellor Anton Wolff von Todenwarth. It is a massive two-storey Renaissance building with a stair tower to the west and a tent roof, standing on a 16th-century square cellar with four groin vaults and a central column. In 1759 Landgrave Ludwig VIII gave the property to his favourite Helene Martini; in 1803 the interior was remodelled and the garden turned into a princely wood store. From 1854 it housed a surgical and eye clinic, and around 1870 the doctors known as the Neuntöter signed a contract with the Alice-Frauenverein, after which the house was extended as the Mauerspitälchen; the Alice-Hospital moved to Dieburger Straße 21 after a new building in 1883.

The building is used today as offices for the Konzertchor Darmstadt and the Darmstädter Residenzfestspiele. Since 1976 the cellar, adapted by the Darmstadt Jazz Club with its own side entrance and sanitary rooms, has hosted concerts. The name Achteckhaus refers to its octagonal ground plan.

The building at Mauerstraße 17 is a listed monument in Hesse. Since 1976 it has been comprehensively renovated, and the cellar received its own side entrance stairway with sanitary rooms so that jazz concerts could be held there. The upper floors now serve as offices for the Konzertchor Darmstadt and the Darmstädter Residenzfestspiele, so visits depend on those users.

The square 16th-century cellar has four groin vaults around a central column. From 1976 the Jazzclub Darmstadt adapted it, adding a separate side entrance stair and its own sanitary rooms so concerts could be held underground.