We were two aging couples [(80 & 72, 71 &69] cruising and we booked this tour through Viator. We had a delightful guide/driver and ended up being only 6 people in the van. We covered 4 'prime' tourist spots: The park with the two tectonic plates, Gullfoss falls, an extinct volcano and a geyser field. We got sufficient time at each stop. We were lucky with the weather, we got sunny breaks at every stop and a few showers while in transit between them. The temperature was as expected 13°-17°C so a light jacket/windbreaker was needed, even though it was not zipped up.
All of the spots were very tourist friendly with walking paths and washrooms not too far.
We put 17,000 steps on my wife's Fitbit on that day.
The park with the tectonic plates was a downhill wooden path with interesting plaques and views all around, we walked essentially between the plates to a meeting point at the bottom. The slope is gentle and easy to walk and enjoy! A great first stop!
Then we went to Gullfoss falls, a beautiful falls! We took lots of pictures of the falls and river. There were more people here, but still not what we would consider crowded. We did not walk to the closets points as there was a lot of mist in the air and we got our fill of great views from the elevated portions of the paved path.
The we went to the extinct volcano and 2 of us walked all around the caldera. From the top we had fantastic landscapes to admire. The walk up and around the caldera is not paved and you have a few climbs and a lot of uneven surfaces to walk, but we have done far worse many times.
Then we went to geyser field, which is quite tourist friendly with paths to walk on around and in between the geysers which some erupt every 6-10 minutes. We also had a lite lunch here fish & chips Icelandic style where the breading is a light charcoal colour! Easily one of my top 5 fish and chips. With 2 baby beers + 2 f&c = 92$ CAD, not cheap, but we would order again!
At the beginning of the tour we also visited a spot where they bake bread in the ground (thermally heated) and we saw spots of boiling mud adjacent to a small lake. Our guided advised us NOT to test the water temperature as it could be scalding hot... 50 feet away a couple were canoeing in the lake.
We were away for a month through Amsterdam, a British Isles cruise, and an Iceland/Scotland cruise and this tour is easily top two experience of the trip [3 tours were outstanding so picking just one is too hard] We have no hesitation in recommending this tour.