Our Iceland trip will be 8 days in August. Our tentative itinerary is as follows:
3 nights in Reykjavik: run the Reykjavik marathon
3 nights on the south coast: 1 day on Westman Island
1 day hiking the Skogafoss trail (this is the 10 mile out and back trail, so will take a major portion of
the day).
1 day to drive up the coast to Dyrholaey or the black sand beaches or even to a glacier lagoon.
This is a wildcard day.
2 nights near Fludir or Havleradir: drive into the highlands and hike the geothermal trails. We would either still in the Kerlingarfjöll Mountain Resort or outside the highlands and spend the second day visiting Geysir, Gullfoss, and other Golden Circle sights.
Please give suggestions on the itinerary. What town should we stay on the south coast or near Fludir? Any recommendations for non-active things to do in Reyjkavik on the day before our marathon? Is the 3rd week of August too late to see puffins? Any other guidance or recommendations will be appreciated.
Definitely get up to Jokulsarlon. The zodiac boat ride there is excellent, we have done that twice. For your highlands time, keep in mind that reservations and service fees are in place for this coming year. Here is a link for the information.
https://ust.is/english/the-agency/news/newsitem/2024/12/17/Reservations-and-service-fee-in-Landmannalaugar-summer-2025?fbclid=IwY2xjawHSnQRleHRuA2FlbQIxMQABHQUkrq-dSjFDqc0DutHfbSlo5jxkCrU2DKoGdnwYyjBYGlGx9GeaZExWyw_aem_PlILyNYQDKaKz8RAu_wKxA
As for where to stay on the south coast, there really aren't many towns, more like little villages. Vik is the largest and there are only 300 people there to give you an idea. Just look at a map and see what general area you want to stop at for lodging, and then on google maps click on the hotel icon and places nearby will show up, or go to booking.com or bungalo.com and use the filters/map.
In Reykjavik itself, things we have enjoyed at the local pools, the food tour, the Citywalk "free" walking tour (tip at the end), Pufa, Hallgrímskirkja church and be sure to go to the top, Perlan, and then just wandering the streets checking out the street art. There is FlyOver Iceland, but we did not care for that, FWIW.
August is not too late for the puffins.