Bir Tawil is kind of a disputed territory, except that it's the exact opposite: both Egypt and Sudan say that the other country has sovereignty over it.
Is it possible for ordinary travellers to visit the place without special permission from Egypt or Sudan? That is, once you've done the necessary paperwork to enter one of the countries, you can get to Bir Tawil. In addition, is it possible to leave one of the countries without entering the other?
If it's not possible, are there any other such places? Wikipedia has a list of such places, but apart from Antartica, the other two ones (both in Europe) seem pretty small.