Hi Marc,
Jim and I rented a car right at the dock. There is an office for Sixt and for Avis (this was three years ago). It is very easy to drive in Iceland. The gentleman at the counter even suggested the route opposite to the ship's tour so we would be visiting the sites ahead of the tours from the ship. (We were on Crystal - no included excursions). Iceland is magical.

The article was amusing. I always study google maps on the computer before we venture out in new locations. Then I use Waze on my mobile phone for driving directions - it worked well in Iceland.