How to get Xcalbur + Achievement.
Excalibur the Sword of Myth
The blacksmith in the Dwarf Cave can make the weapon for you. You reach this place in the game early on, but he can’t make you the weapon because his supply of Adamant is exhausted.
Sadly, you don’t get any Adamant until way later in the game. You can find some inside a chest in the Sky Castle.
Once you have it, take it back to the blacksmith, and he’ll make Excalibur for you. Only a Knight can wield it.