We were on a Holland America cruise to Norway last May with our then 22 year old daughter and loved Oslo. It is a very walkable city that you can do on your own. We took the ferry to see the Norwegian Museum of Cultural History and enjoyed walking through the neighborhoods to get there. The museum is spread out over many acres with many buildings to explore, including a Stave Church (great to see if you have any Disney Frozen fans) and lots of farm animals. We then went to the Akershus Fortress (again, if you have any Frozen fans, worthwhile to see) and the Resistance Museum (husband is a fan of WW II history). Lots of walking but so worthwhile.