Pwll Dwfn (English: deep pit, pronounced [pʊɬˈdʊvn]) is a cave in the Black Mountain, South Wales.

It is located in a dry valley northwest of Dan yr Ogof and cavers can access it from the show cave's car park.

[1] Pwll Dwfn is one of the few caves in the area which requires single rope technique (SRT).

The cave is terminated at the bottom by two static sumps and has colonial coral fossils on the walls.

In 2011 a new passage was als found at the top of pitch 5, ending in a sand chamber and a boulder choke.