Gollum's cave

Gollum's cave was where Gollum lived for hundreds of years before losing the Ring to Bilbo Baggins.

The cave was located under the Misty Mountains near Goblin-town. It was close to the Great Goblin's cavern by following an estimated thirty miles of long dark, and narrow in some places tunnel.

About four hundred feet in diameter, the cave was a natural creation formed by water that had seeped through the rock dissolving some of it. The result was a cavern with a small lake in it. Its main features was a small island at its center, a narrow shoreline, and an underground stream from which the lake water drain to the outside.

Gollum's history there
After he was exiled from his family in the late twenty-fifth century of the Third Age, Gollum sought shelter from the Sun under the Misty Mountains. Following an underground stream, he made his way to a dark cave and feeling safe there he made it his home. For hundreds of years he lived there completely alone and lived off the fish that lived at the bottom of the lake, and returning home to sleep on the small island at the center. He also soon found out that Goblins were living close by and would sometimes come through the tunnel. When he felt bold and hungry enough, Gollum, using his magic ring that made him invisible attacked and straggled them and then ate them.

Then in TA 2941, Bilbo on his travels with the dwarves stumbled into the cave after finding Gollum's ring. After a long game of riddles and a promise to be shown the way out, Bilbo, fearing for his life narrowly escaped on his own using the ring to hide himself. Gollum soon left the cave that he had called home for so many centuries to search for the ring and the thief Baggins, and would never return there again.