Been there twice and a day and a half for me is about a day too much in what to me is one of the world's most boring and expensive cities. Iceland's lures lay outside of town - the hot pools, geysers, etc.

and that bus ride in from Keflavik Airport - like driving thru the moon - not a tree in site and just volcanic detritus.

Watching the fishing boats come home was my favorite thing to do in Reykyavik.

I highly recommend the National Museum. www.natmus.is

Also, because your day is at the end of the trip you have the whole trip to meet new people and ask them what is their favorite thing to do in Reykjavik.

the open-air swimming pools heated by thermal heat from the ground are very popular.

Definitely include a visit to Gulfoss Falls - it's beautiful!

Thanks so much for your input. I will definitely look up all the suggestions.

laurie-ann got in first with her recommendation of the national museum of Iceland - here's the link:

http://www.thjodminjasafn.is/english

even better, all the info is in english as well as icelandic and the exhibits are fascinating, from life-size boats of old explorers, to costumes to try on, to DNA research into the origins of the population [turns out that the men are from Scandanavia, the women are celtic, so all those tales of rape and pillage were true!]. it's really excellent and has a good shop and cafe too.

i would also agree about seeing Gulfoss, but i suspect that your tour will take you there as it is part of the golden circle, where everyone goes at one time or another on a trip to Iceland. but if they don't, make sure you see the geysers and phingvellir [excuse lack of icelandic spelling] which is not only the site of the ancient icelandic parliament, but also where the american and european tectonic plates meet. you can walk in a chasm between them, which we thought was quite a thrill!