Yes, you're in Germany and don't know about existence of those "ghost cities", there're some mini "ghost cities" in Vietnam too.
The developers paid much to residents for their land, and call for investment in hope selling at booming price. Money from the banks, the investors flow into the "ghost, bubble real estates" and prices down and down.
The developers run away, banks and investors ( whose money from banks too ) lost their money and "ghost city" for as many as 1 million people stand still there, unfinished, no living...