Right now in Berlin, from the of 9th September until 7th October, Virgin Express is running the worlds longest outdoor billboard, no less than 1100 meters! The ad stretches from Kaiser-Wilhelm-Gedächtniskirche to the Zoologischer Garten.

Written in German of course, as copywriters there are blessed with a language that has words like Rindfleischetikettierungsüberwachungsaufgabenübertragungsgesetz and could probably make a five word headline cover the entire 1100 meters without breaking a sweat. ;)
Actually the headline repeats the core message over and over - you can fly from Berlin to Brussels as from 41 Euros - in between jokes to entertain the pedestrians walking by.