Viking has a host of excursions daily and always one for free while some range from walking tours to helicopter rides to see the glaciers. You can signup for one of theirs or arrange with locals for others. We took our first and last big bus tour to see a local museum of outside houses displaying Icelandic living over the years with locals in character. Followed by afternoon tea.
We embraced the nordic bathing routine and developed a daily process including the hot tub, steam room, snow room and sauna while working in the breakfast, lunch, and dinner.