Lummelunda caves (or Lummelunda grottorna in Swedish) are quite famous for the dripstones down there. I think some of it is only hype - when we got there, it wasn't THAT amazing. Nice, of course, but not that much... Well, anyway, you must have a guide (I wouldn't like to get lost there!), and I guess they all speak English. I think it's possible to take a small cruise there as there's water in the caves plus the humidity. It's also very cold, so even though it may be sunny outside, you'll freeze without a sweater.