Interesting day trip from Reykjavik, although I went for a long weekend just for the diving. You get to scuba dive along the volcanic cracks where the European and North American plates meet. Utterly fantastic visibility of 100m or so underwater. You get guided through and can hire all equipment. The more experience you have beforehand the better to enjoy it rather than fight a hired drysuit for the first time. If you show you know enough they may take you to the lower levels, which are up to 40m deep and totally enclosed - great fun, but not for everybody. Go in wintertime as it is quietest then.
Send your feedback or queries to email@example.com