The nyckelharpa is a stringed instrument from Sweden that is played with a bow. It has been documented going back over 600 years.
In Swedish, “nyckel” means key, and “harpa” was a word for a generic or basic instrument — some open strings on a box.
There is a lot of good information about the nyckelharpa at the http://www.nyckelharpa.org site of the America Nyckelharpa Association (I am a proud member). Also see http://www.cadence.nyckelharpa.eu/home/nyckelharpa for more nyckelharpa background, as well as other pages at http://www.cadence.nyckelharpa.eu.
There are a number of videos on YouTube with nyckelharpa. One of my favorites is Magnus Holmström at https://www.youtube.com/watch?v=D93OD5IYDx4&index=30&list=FLR7qxZX4Sl9SUprTrizodiw.