Cracks of Doom
The Cracks of Doom, also known as Sammath Naur, was the forge and workshop of Sauron tunneled deep into Orodruin and open to its central fire. It was here that Frodo Baggins cast the One Ring to be destroyed.
The name is a wordplay on "cracke of Doome" (Macbeth; IV i 117) meaning the "sudden sound (crack) of the trump that announces the Last Day".
Of course Tolkien uses here "crack" to mean "fissure".