The thing about black holes is, they're big and they're black and they're deadly, and you'd have to be mad to go anywhere near them. Because anything that falls inside a black hole ends up crushed in the singularity.

Unfortunately, the Doctor just went mad, or so it seems, and flew his TARDIS beyond a black hole's event horizon, causing him and his companion Lucie Miller to end up marooned on a planetoid just inside the event horizon. Along with a Dalek saucer... and something else. Because this is no ordinary black hole...

This is the Cradle of the Darkness.

Doctor Who: The Dalek Trap (DWM583 promo) | Big Finish Productions