I always wondered why bikes were so popular in Europe.

Two Dutch girls are riding their old rickety bikes down the back streets of Amsterdam one late afternoon. As it gets closer to dusk and the old streets start getting darker, the two girls start riding faster, looking more and more flustered and out of breath, when one girl turns to the other and says, "I've never come this way before!"

The other girl smiles and says, "It's the cobblestones."