What's the name of another troll movie?

I've been trying to remember the name of another troll movie, and everytime I ask somebody, the answer with 'A Troll In Central Park' (which is a really cute movie and I liked it too when I was younger).

What I remember from the movie is that the trolls live underground in this really watery, dark, glowy kingdom place, and both a boy and a girl are trying to find them. The poor, country boy uses a ball of string so he doesn't get lost. He eventually gets found by the trolls, and he gets put in a cave, but he sings and jumps on their toes, which really hurts them for some reason.

The girl is a princess, I think, and she goes through a tiny door when she notices a glowing pinkish red rose glowing on it. She sees her great god/grandmother or something there, and she's spinning thread, and later she gives her a magic ring that has almost-invisible thread. She uses this to not get lost in the troll caves too.


Help, please? It's driving me insane!