Try listening to the following Youtube video.
They are usually highly decorative with inlaid mother of pearl or bone in the fingerboard and rosing on the body. This one (see the pics below) was made by Sveinung Gjovland in 1956. It is stunning. It has a very thin front and thicker back. The bass bar is different from a violin and this particular fiddle has a very big sound for a hardanger. I have been playing it while I have the chance - not the first instrument that comes to mind for the blues though!
As I have developed my interest in playing the fiddle, my partner has developed a fascination for how they are made. He now teaches violin making to amateur makers.
We also started developing an interest in Scandanavian folk. So I take the opportunity to go to hardanger workshops when I can. One thing leads to another and we are in the middle of making a hardanger ourselves. Fingers crossed it turns out as well as this one!
It took us about three years to draw together the information and we have now developed our own plans. This traditional hardanger has given us some more ideas about to develop and finish ours.