What is the Noche en Blanco in Madrid?

Noche en Blanco, or White Night in English, is an all-night cultural extravaganza which takes place on one night each September (in 2009 it will take place on the night of September 19) in Madrid. Everything is free of charge and the city puts on 24-hour public transport to make getting between events easier.
Begun in Paris as 'Nuit Blanche' in 2002, the even has since spread to numerous European cities, as well as Sao Paolo, Toronto, Montreal and Chicago and is known as Light Night in Leeds.

It is based on a similar German event, known as Long Night of Museums (or, more precisely, Lange Nacht der Museen).