So, I would normally be the first to say I am not at all a fan of Annbjørg Lien. She is way after my time. But, this one video of her is actually a very good introduction to the hardingfele, which would be my next instrument if I didn’t live in the US.
You will notice the extravagant ornamentation first. But, look at the depth of the F-holes. Also, the fele has 4 playable strings and 4 – 5 drone strings under the finger board that vibrate in sympathy.
Here is a crazy 15-year-old playing a more energetic, albiet more difficult to hear version of the same piece:
There is no standard tuning. Each region of Norway developed several. So, effectively you retune all 9 strings for each piece. Here is a short piece that really exploits the drone strings. They effectively give the alternating parts two different voices.
Here is a nice piece from Bukkene Bruse (I need to write an article on them some day):
You should also take a look at Martine Lund Hoel: