Icelanders, like many islanders, are self-confident and reserved, but once you break the ice, so to speak, they are among the friendliest in the world. Of course, they, too, have their extremes. Although weeknights in Reykjavik, the capital city, are usually quite sedate, the wee hours during the weekends (particularly Friday nights) can get downright raucous as stylishly dressed young people observe a rowdy party-on-the-streets ritual known as the runtur, or circuit.