Also known alongside the Anvil of Mithas, with which it is twinned.
The Hammer of Gharen is the only object strong enough not to shatter when used to shape metal upon the Anvil of Mithas. When the Hammer strikes the Anvil, it produces a ringing which reveals the location of the entrance to the Dwarven mines beneath Red Mountain.
See Anvil of Mithas for full history and rules.