Palacio Dassen, Historical mansion in Monserrat, Buenos Aires, Argentina

Palacio Dassen is a historic mansion in Monserrat completed in 1914, distinguished by a prominent tower structure. The building is notably narrow but extends deep into the lot, and features an astronomical observatory at the top accessible by interior stairs.

The building was completed in 1914 by architects Alejandro Christophersen and Claro Cornelio Dassen, initially serving as both a residence and automobile showroom. It later became headquarters for the Argentine Actors Association and received national historic monument status in 1999.

The tower was conceived as a private astronomical observatory and as a lookout toward the Río de la Plata, reached by a staircase of 365 steps. Since 1983 the building has housed the Asociación Argentina de Actores, so the former family home is now a working union headquarters.

The building stands at Adolfo Alsina 1762–1766, between Solís and Entre Ríos streets, on a lot only 7.6 m wide but 55.66 m deep. Since 1983 it has been the seat of the Asociación Argentina de Actores, so the interior is not open as a museum; visits depend on the association. The tower observatory is reached by a 365-step staircase.

The tower rises almost 60 metres and is reached by a staircase of 365 steps. It was built as a private astronomical observatory and as a lookout towards the river, when low houses still surrounded it in Monserrat.