Any jaunt to Iceland — be it of the lengthy or brief kind — cannot be complete without a trip to the land's famous Blue Lagoon. Halfway between the airport and Reykjavík, the geothermal hot springs are best visited on one's way to or from the airport.
Despite being a bit of a money pit, you can avoid extra costs by bringing your own towel and robe, shelling out a mere €35 compared to €50+ for the inclusion of a beverage and a mask. Instead, swim over to a silica stations while in the lagoon and resist the urge to drink.
I was lucky to make it for sunrise, which made for an excellent post-flight refresher and a rather breathtaking arrival in Iceland.