Escaping from a colon-lettered drive

As I already found out, it's possible for drives to have letters that aren't letters. Some symbols are more interesting than others, especially the colon. You'd think that you could change to such a drive by typing two colons at the prompt, but that's actually interpreted as a line label and does nothing. To change to that drive, you need to do cd /d "::\". Also interesting is that typing c: to go back to the C drive from there sometimes works and sometimes has no effect. cd /d "c:\" always works, though.