Originally, an underground cavern, the Cave of Adullam was near the town of Adullam. This is the cave where David hid from King Saul when Saul sought to kill him. What's more, it wasn't far from where David slew the giant Goliath, in the hills of Judah.
I Samuel 22:1-5
David left Gath and escaped to the cave of Adullam. When his brothers and his father's household heard about it, they went down to him there. All those who were in distress or in debt or discontented gathered around him, and he became their leader. About four hundred men were with him. (NIV)