Sandvika
"Kystleden" offers self-service cabins for rent located in the Oslo Fjord.
The cottages are popular because of their excellent locations, and are meant for enjoying the nature. Usually there is a rowboat for the guests to use.
The self-service cabins must be booked and payed in advance - see the web site for more information. You can book on the web or by contacting the Oslofjord Outdoor Recreation (OF)by phone + 47 67 55 49 90.
The guests are obliged to clean, before they leave. Usually you must bring your own sheet and sleeping bags.
Source: Visit Greater Oslo