The Cave

Was the cave where Voldemort hid the locket already magical or did Voldemort create it to hide the Horcrux?

In HBP, Dumbledore describes an antechamber cave with another larger cave containing the lake. It’s unclear where Voldemort actually brought those children, but it’s possible it was all the way to the interior island.

In DH, Kreacher describes Voldemort bringing him there to drink the existing potion before the locket was placed in its hiding spot.

Does Rowling ever explain whether this cave was just a natural formation Voldemort used as a hiding spot or if it already had some of its features before Voldemort got there? (Ie Inferi, Potion) It sounded like Voldemort put in the blood wall portion and likely added the inferi. However, with how those kids came out of the cave, is it possible the potion predated Voldemort?