Karl Johans gate is the main street of Oslo, and to log the cache some easy tree climbing are required. Look at the spoiler picture, if in doubt.

Karl Johans gate

Karl Johans gate is the main street of the city of Oslo, Norway. The street was named in honor of King Charles III John, who was also King of Sweden as Charles XIV John.

The street includes many of Oslo's tourist attractions: In addition to the Royal Palace, Central Station and Stortinget, there are the National Theatre, the old University Buildings, the Palace Park and the pond ("Spikersuppa") at Eidsvolls plass, which serves as a skating rink in winter. Oslo Cathedral's lower end is surrounded by the Bazaar Market (Basarene ved Oslo domkirke), which is integrated with the historic Fire Watch (Brannvakten) that served as Oslo's main fire station from 1860 until 1939.

Source: Wikipedia