This is how Virgil describes it in Aeneid VIII:
iam primum saxis suspensam hanc aspice rupem,
disiectae procul ut moles desertaque montis
stat domus et scopuli ingentem traxere ruinam.
hic spelunca fuit vasto summota recessu,
semihominis Caci facies quam dira tenebat
solis inaccessam radiis; semperque recenti
caede tepebat humus, foribusque adfixa superbis
ora virum tristi pendebant pallida tabo.
Now first of all look at that cliff, all overhung with rocks, and see how the great bulk of the mountain has been scattered far and wide, and how that cave lies deserted and how the crags speak of some great destruction. Here was the cave, sunk deep down into a vast cavern, where the dreadful form of the half-human Cacus used to live, inaccessible to the rays of the sun; the ground was always warm with fresh slaughter, and, fixed to the haughty door frame, hung the faces of men in gloomy decay.(Aeneid VIII, 190-197)
If you imagine some dismembered heads hanging by the entrance I think it's not a bad match.