A mostly forgotten instrument born around the time the opera was born in Florence, in the late 16th century. The audio starts a bit late, but give it a chance. I'll find another video with more playing, as this one is mostly just an explanation of the instrument. (Though I don't understand why the first set of tuning keys is eight in number if the fretted set is only seven. Hmmm.
Here' a nice one:
Okay now let's get trippy...with the theorbo.