Reykjavik is a beautiful small city. Besides being spotless, it has some beautiful architecture and some great cafes to enjoy the day in. The tallest building is the big Lutheran church and can be seen from anyplace in Reykjavik. It is a good guide in case you think you are lost there. From the top of the church you can see all of Reykjavik, including the Tjornin Lake, where many take their children to feed the numerous ducks and sea birds that are gathered there.
Reykjavik is VERY expensive so bring lots of cash if you are going for an extended period of time. Nightlife is great, espcially on weekends. Lots of artists and young people around. Everyone is very friendly!