This post consists basically of spoilers, so you should stop reading now if you don't want to be spoiled :)
In most Known Space stories we are told that you can't use hyperdrive inside gravity wells. Ships that do so just disappear never to be seen again.
In Ringworld's Children, Tunesmith broke this "law". He dropped into hyperspace inside the Ringworld's sun well and survived. He explains to Louis that there's a whole ecology that grew within dark matter, and ships are eaten by predators from this ecology.
In The Borderland of Sol Bey does some wild speculations about the possibility of "hyperspace monsters" eating ships. Like me, Carlos Wu doesn't like this explanation.
Later when the protagonists went near a large mass on the borderland of Sol, their hyperdrive actually disappeared (without any exit hole or anything) and so they simply dropped out of hyperspace.
Carlos explains that using what he claims to be a well-established model of what happens when ships hit such a singularity. According to that model, a low gravity gradient (which is supposedly something you find on things like stars and planets) would disperse the ship's atoms across its path; but an extremely high gravity gradient (like that from the black hole used by Julian Forward) could just snatch the hyperdrive out of the ship like that.
However, this flies in direct contradiction of the "hyperspace monsters" theory. On top of that, hyperwave communication is known to not work within gravitational singularities. This doesn't fit with the "hyperspace monsters", unless they are also "eating" the waves near the source.
So, are there "hyperspace monsters" or not? Was Tunesmith lying?