This question struck me while reading The Hobbit (again). It is stated that Thranduil uses 'magic' doors and that no one can escape them.
Anyone willing to explain, because I certainly am muddled.

By the way, I'm not talking about magic like the Palantir or the 'magic' that Galadriel uses...I'm talking about that Harry Potter kind of magic where...well, the doors are simply sealed by magic