Treehouse on the Berlin Wall, Wooden architectural structure near Mariannenplatz, Berlin, Germany

The treehouse near Mariannenplatz is a two-story wooden structure built from salvaged materials and scrap pieces tucked between two trees. It fills a small triangular plot with practical living space created through resourceful construction.

Turkish immigrant Osman Kalin built this structure in 1983 on a small plot that sat between East and West Berlin. The location was technically in East German territory yet remained accessible from the western side.

Osman Kalin, a Turkish immigrant who moved to Berlin in 1980, built the structure and used the plot to grow fruit and vegetables, watering the beds mainly with rainwater since the site has no water or electricity connection. The plot is nicknamed the "Gecekondu of Kreuzberg", after the Turkish word for a self-built house, and a children's book, Osmans Garten, tells his story.

The treehouse sits within walking distance of Görlitzer Bahnhof U-Bahn station on the U1 line, with the walk heading north along Bethaniendamm. The location is accessible but sits on a small corner plot that can be easy to pass by without noticing.

Kalin gave the house the imaginary postal address "Bethaniendamm Nr. 0, Berlin 10997" himself; no authority granted it. The plot was never formally reassigned to Kreuzberg either, despite media reports of a 2004 boundary adjustment.