The issue actually comes in two separate parts.

First, some maths say that if you jump into any black hole, they might be connected to other universes. The problem with most of them is that once you jump in you're on a collision course with the singularity, which means that tidal forces will tear you apart and then you'll eventually fall into nature's divide by zero error. So you can maybe see something, but you're not able to communicate with the outside world and you'll be destroyed in the not too distant future. Obviously this is less than ideal.

Then as mentioned, if the black hole is spinning in just the right way, the singularity can be a ring instead of a point. If that's the case, you may be able to fall through the hoop instead. This is just a way to do the above and not die, although it's very tentatively theoretical right now.

Relevant wiki link, if you want the idea without too much math.