The lute, huh?
Well, the violin is a little difficult to pick up at first. But, once you've gotten past the squeaks and off-pitched ugliness it's quite... fulfilling. And stimulating, if you're playing a really fast song and trying to stay on top of it. Hard to really describe it properly.
Depending on what you choose and how much of a self-starter you are, you'll also need a teacher. Can you read music?