In the evening Saturday 21st of August the Reykjavik Culture Night is planed. Held yearly since 1996, Menningarnótt celebrates the city’s "birthday". The festival is usually made to coincide with the Reykjavik Marathon, in the month of August. The majority of Icelanders flocks to the city to celebrate on this night, and the streets take on the air of a carnival, replete with clowns, fire-eaters and other amusing entertainers. The festivities are numerous, all shops, restaurants, coffees and galleries’ will be open until late night and a rock concert is planed in central Reykjavik. A spectacular display of fireworks over the harbor at 11pm brings the festivities to a close, although the party continues on into the wee hours of the morning.
So just promenade the streets of central Reykjavik and I am sure that you will be surprised. If you are planning to dine out that evening, do reservation right away or be prepared to wait unless you are early in and ready to be served between 6 and 8 pm.