The Sea of Glass
Revelation 15:2-4

"And I saw as it were a sea of glass mingled with fire: and them that had gotten the victory over the Beast and over his Image and over his Mark and over the number of his name, stand on the sea of glass, having the Harps of God.
And they sing the Song of Moses the servant of God and the Song of the Lamb, saying, great and marvelous are thy works, Lord God Almighty; just and true are thy ways, thou King of Saints. Who shall not fear thee, O Lord and glorify thy name? for thou only are holy! for all nations shall come and worship before Thee; for thy judgments are made manifest."