Hochhaus Union Investment, Brutalist office building in Bahnhofsviertel, Frankfurt, Germany

Hochhaus Union Investment is a 93-metre office tower in Frankfurt's Bahnhofsviertel, built in 1977 to plans by Speerplan Regional- und Stadtplaner GmbH and Neue Heimat Städtebau Südwest GmbH. It has 19 upper storeys and ranks 36th among Frankfurt's high-rises (2014). At night the facade is lit in blue and white.

The tower was built in 1977 to plans by Speerplan Regional- und Stadtplaner GmbH and Neue Heimat Städtebau Südwest GmbH, not by Albert Speer personally. Union Investment sold it in November 2014 to GEG German Estate Group, which announced conversion to housing. In April 2021 DIC Asset sold it to developer Groß & Partner, which in March 2023 announced a renovation as offices under the name Kaia, with the atrium to be demolished and replaced by a timber-hybrid new building.

The building displays brutalist design with raw concrete surfaces and visible structural elements that define its architectural expression. This style shapes how the neighborhood looks and appeals to those interested in modern architecture.

The tower stands in the Bahnhofsviertel, a few minutes on foot from Frankfurt's main station, so it is easily reached by regional and long-distance trains as well as by tram and U-Bahn along the nearby Kaiserstrasse. The site is a short walk from the banking district and the old town. The atrium is to be demolished and replaced by a timber-hybrid new building under the Kaia project, so access may be restricted during works.

At night the building is highlighted by blue and white illumination, making it a distinctive point in the nighttime skyline. This lighting gives the raw concrete a different quality than during daylight hours.