The War and Peace Museum is a privately owned museum by the road in Hvalfjordur.
The museum traces the unique and remarkable history of occupation from 1940 to 1945, a story that transformed a more peaceful countryside into a setting for world events and was crucial to the Allies' victory during World War II. Here you can see an elaborate collection of monuments and memorabilia related to the history of the occupation of Hvalfjörður during these fateful times of turmoil. You can also see here a number of items belonging to the Russians, Germans and Italians.
Unlike many museums, the setting here is cozy and friendly, it's cramped in a delightful way. Also, there is an excellent café here which I recommend to visit.
The cache is not inside the museum but on its property, with a permission from the owner, Gaui.