Defense Against the Dark Arts teachers. Or in the Carrow's case, just Dark Arts. Wow, there really must be a curse on the Defense Against the Dark Arts position, all of these teachers either died or had something bad happen to them.
Ice cave in the Skaftafell National Park in Iceland. Ice caves collapse and new ones form as each glacier grinds slowly towards the sea. Local guides can help you (without dying) find one. (Visit Skaftafell National Park in Iceland.