I will be stopping at Grundarfjorour, Iceland as part of a cruise in Summer of 2025. I want to see Kirkjufell mountain and the Kirkjufellsfoss Waterfall. Are there any local tour operators in Grundarfjorour that could take us there or is it walkable (looks like 45 minutes on Google maps). Thanks in advance for any advice.
I'm assuming you mean Grundarfjörður. (Ð/ð is a consonant and not at all related to O)
But to see Kirkjufell you don't need to do anything except look in the right direction, it is (weather permitting) visible from the port. I don't know if there are any tour operators, but of course it's walkable to Kirkjufellsfoss, there is a path that leads to the waterfall.
You can easily walk there. My husband did this just this past summer and then walked around the mountain as well, and then back to Grundarfjordur.
Unlike most cruise ports, your plan is practical here. Kirkjufellsfoss is a long-ish, but mostly level walk from the ship. We had walked into town, and "rented" annoying and dangerous electric scooters scattered carelessly around town, to save our aging legs. You can see Grundarfoss from the port, and while it is closer, it requires a long, unpaved, uneven "meadow" walk from the road. Although Kirkjufellfoss is up a small hill, it has gravel paths, one of them steeply sloped. Google Maps is pretty accurate here. (I believe Kirkjufell Mountain is not suitable for unguided walkers without equipment.)
At my age, it is a significant fact that NEITHER of these two waterfalls has a TOILET building at the site!
You should check a climate website for the expected temperatures and weather during your visit. There are more details if you are willing to dig through my trip report:
https://community.ricksteves.com/travel-forum/trip-reports/western-iceland-by-car-summer-2023