Nikolaikapelle, Medieval chapel in Hietzing, Austria

Nikolaikapelle stands on the eastern slope of Nikolaiberg at 268 meters elevation with a rectangular base, three large windows, and bluish-gray plaster. Its simple structure and compact footprint make it an unpretentious building that fits naturally into the hilly landscape.

The Nikolaikapelle was probably built in the late 12th century and first appears in a document in 1321. Its surviving wall-and-ditch system suggests it stood at the centre of a high-medieval castle complex. Renovated in 1735, it was profaned in 1787, damaged in 1809 during the Napoleonic Wars, and restored in 1835–1837 on the orders of Archduke Ludwig.

The chapel is dedicated to Saint Eustachius, a name chosen in 1837 that reflects its role within the Lainzer Tiergarten hunting grounds. This change in dedication shows how the building's meaning shifted over time for the people around it.

The chapel stands on the eastern slope of Nikolaiberg, near the Nikolaitor entrance to the Lainzer Tiergarten. It is not open as a regular visitor site; the Eustachius mass is held around 20 September each year, either in front of the chapel or in the church of Mariabrunn. The building itself has been without furnishings since 1945.

The chapel's name comes from Saint Nicholas: "Nikolai" is the Latin genitive of Nikolaus. The name later passed to Nikolaiberg, the Nikolaitor gate, the Nikolausgasse, the Nikolaisteg footbridge and the Nikolaibrücke over the Wienfluss. The chapel itself has been dedicated to Saint Eustace since its 1835–1837 restoration.