We just got back from 4 days in Iceland. It was a wonderful trip, very busy - lots of driving.
We stayed one night at Hotel Berg, very chic modern hotel near the airport, very comfortable. Then we stayed two nights at the Lighthouse Inn due to the free breakfast, which was also great, more of a cozy cabin vibe. We used our airmiles for accommodation and there were no choices in Reykjavik.
Most people seem to follow the same itinerary. We had a red eye from Canada so after picking up the hire car went straight to the blue lagoon for chill time. We lucked out and had a gorgeous sunny afternoon there. If I go again I plan to visit the Sky Lagoon.
After that we spent some time exploring the new lava fields around the blue lagoon area.
First night we went into Reykjavik for dinner and a walk around (in summer it's light until 11ish), saw the church, rainbow road etc
Second day we did the South Coast (which I prefered to the Golden Circle), black sand beaches, waterfalls, glacier, had dinner at a charming restuarant Gamla fjósið before heading back to hotel and straight to bed.
Third day we did golden circle (were supposed to do Whale watching but this got cancelled due to wind), geysirs, national park, waterfalls etc, a lot busier on this route. Dinner in Keflavik at the Library bar (decent).
Last day the whale watching got cancelled again so did the Lava show which was interesting, then did some more reykjavik sites art museum, shopping etc, before heading to airport.
Top tips are find a good bakery to fill up on sandwiches, and tasty treats. We loved Kökulist bakery near the airport.
We did a lot of sightseeing on our trip, but next time I would do more specific experiences eg walking on glacier or ice cave visit.
I'm glad we were there in summer despite no northern lights viewing, the long days make it so easy to fit a lot into each day.