The present invention relates to a system in a watercraft or a section thereof or in another structure or a section thereof for providing furnishings at least partially, which system comprises a number of prefabricated room units and a watercraft or a section thereof or another structure or a section thereof, and which system comprises one or several room units to be inserted into the watercraft or a section thereof or other structure or a section thereof, and which system comprises room units, the exterior side portion of which forms a part of the outboard of the watercraft or a section thereof or other structure or a section thereof and/or the interior side portion forms a part of the open inner section of the watercraft or a section thereof or other structure or a section thereof. Moreover, the invention relates to a method for providing furnishings at least partially in the system according to the claims, which system comprises a watercraft or a section thereof or another structure or a section thereof and at least one prefabricated room unit, according to which method at least one room unit is inserted into the watercraft or a section thereof or another structure or a section thereof and moved on the watercraft or a section thereof or other structure or a section thereof into its predetermined position.