After Keflavik, where?
 

Our flight arrives at 6 AM. We will drive to our first Airbnb in Hvergerdi that afternoon and have free time that morning. Not really interested in Blue Lagoon...we may visit there on our last day. Any other ideas, sightseeing, etc.? Our last two nights (it’s a 7 night trip) will be spent in Reykjavik. We enjoy short hikes, history, music and craft beers, although it may be just a bit early for beers! We will have a car. Thank you!

What time of year?

March 8.

Well Keflavik, besides being the airport is also a tiny village. There you can visit The Viking world of "Vikingaheimar" which provides a replica of how the Vikings used to live. It was very cool and if you are keen on history, then you'll love it.

Here I found a couple of ideas you may like as well.

Thanks
 

Thanks all for great ideas. Can’t wait!