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."