In J.R.R. Tolkien's The Hobbit, what is the name of Smaug's lair?

Smaug's lair in J.R.R. Tolkien's The Hobbit is the Lonely Mountain.

The Lonely Mountain, also called Erebor, is a prominent peak and a former Dwarven kingdom in the north-east of Middle-earth. Smaug occupies its halls after driving out the Dwarves, taking their treasure and ruling the surrounding region through fear.

The mountain is not merely a cave or a natural landmark. It contains the great halls of the Dwarves, the hidden Front Gate, and the secret passage that Bilbo uses during the quest. The Arkenstone, a precious heirloom of the royal line, is also found within Erebor's treasure hoard.

Mount Doom is a different volcanic location in Mordor, central to The Lord of the Rings. The Misty Mountains and Iron Hills are also separate geographic regions, so they are not Smaug's lair.