The heaters' tunnel under the Zimmerstraße

Manfred Höer worked as a heater for the East Berlin electricity company BEWAG in an office building right on the border near the Mauerstraße and Zimmerstraße. Its cellars next to the border were locked and sealed, and were inspected only about once a month, most recently in mid-December 1971.

He knew where the keys and the sealing tools were kept in an unmanned porter's lodge. With his brother Peter and his friend Peter Schöpf he broke through a 60 cm cellar wall and dug a tunnel about 20 m long and 60 × 60 cm in cross-section, spreading the spoil in the neighbouring cellar rooms.

In the early hours of 9 January 1972 they broke through the pavement just in front of the Wall; the empty plot two steps away already belonged to Kreuzberg and West Berlin.

The next morning another heater found the building cold, sand in the boiler rooms and the seal missing from the border cellar, and alerted the police. The Stasi found the tunnel, but a search for the three men in the GDR came to nothing.