The "Waterküken" a 30 square meter house is one of the most expensive houses in the world.
It is currently on the market for 6.3 Million Euro (9.35 Million dollars).
It's 200,000 Euro (296,000 dollars)/square meter.
If the city grants a building license the house will be worth 8.5 Million Euro (12.6 Million dollar)
Links: www.abendblatt.de, www.morgenpost.de