In the 1980s, a Turkish worker in Germany, Osman Kahlin, provoked controversy when he turned a patch of disputed land against the Berlin Wall into a makeshift farm.
The land was owned by East Germany, but lay on the Western side of the wall due to a quirk in the wall's hurried construction.
Kahlin fought a running battle with both East and West German police to keep hold of the land, and kitted it out with a fully functioning treehouse that became a local symbol of resistance to authority.
Alex Eccleston speaks to Osman's son, Mehmet. A Whistledown production for BBC World Service.
(Photo: Osman's treehouse. Credit: Schlemmer/ullstein bild via Getty Images)