The dusseldorf fair on the banks of the Rhine. europes largest travelling fair. About 7 square miles of beer tents, bars, bands, rides, nightclubs, fireworks, food stalls, currywurst, great atmosphere, kicks shit out of crap like Thorpe park etc.
A ride down the Thames on a boat, Tower of London, I would have also said Niagara and Grand Canyon. Ephersus (Google it if you have no idea), I would have said the World Trade Centre but .... Golden Gate Bridge (yes I know it's not the largest).