First stop was Snorkeling at Silfra Springs. We headed into Thingvellir National Park which is very crowded. The snorkeling experience was awesome swimming in between the shifting apart continental plates. The water while cold is the clearest in the world and it was an amazing experience.
Our snorkeling guide gave us two very good recommendations for the rest of our day in Reykjavik. First was to eat at the restaurant Public House, highly recommended. Second was to visit the Reykjadalur Hot Spring Thermal River. This is a little over an hour drive outside of Reykjavik and about an hour hike into the river, but it was totally worth it. We went there in the evening and we had the whole river to ourselves.
We stayed at the Icelandair Hotel Reykjavik Marina which was very nice and in a great location to be able to walk to tons of restaurants