Well, moving right along, I should repeat what I've heard about Kerr ( spinning ) black holes. The problem with Schwarzschild black holes is, of course, that exploring them is strictly a one-way trip; once you pass through their Schwarzschild radius, you are doomed to fall right on in to the singularity.
Not so, apparently, with a Kerr black hole if it is spinning fast enough. Then the singularity is in a ring (sort of) and you can in principle plot a trajectory through the middle of the ring (or something like that) and come out the other side. Except that ``the other side'' may not have any resemblance to where-when you went in on this side! This has already been used as a great gimmick for SF stories involving time travel and other apparent logical paradoxes. I don't understand it at all, and I doubt very much that anyone else does, but one can always postulate that someone will, someday, and use it for practical(?) purposes. After all, as Arthur C. Clarke says, ``Any sufficiently advanced technology is indistinguishable from magic.''