Some say that a black hole is a rip in space-time, a portal linking two points in the universe as one. How sound is this? I've read that when a giant star collapses, what is left behind (a massive neutron star?) is so dense that light cannot even escape its gravitational pull. Is this phenomenon caused by an actual object? If one were to travel into a black hole, should not one find only really dense matter?
There should be nothing special about crossing the "event horizon" - the line beyond which light cannot escape and so, in theory at least, one might "travel into a black hole" and not be aware of any physical changes at all.
However, I suspect what you mean is what would happen if one travelled to the centre of a black hole. Here we may speculate but our current theories of physics breakdown at this "singularity" and so we cannot know - nor is it easy to think of how we might design an experiment, given our currently available technologies, to test any theory we have.