The Hall of Origin (Japanese: はじまりのま Hall of Origin) is where the legendary Pokémon Arceus resides.
It is an event-only area, accessible only to players who have obtained the Azure Flute, located above Spear Pillar. When the player has the Azure Flute and returns to Spear Pillar after defeating the Elite Four (as the event will not be possible until after Team Galactic has been vanquished and Dialga, Palkia, or Giratina has been captured or defeated or fled from), the flute will make a sound. After blowing into the flute, a staircase will appear leading up, out of sight.
Following the staircase up leads to a glass-like platform, high above Spear Pillar, where Arceus awaits the player's challenge at level 80, the second highest level any legitimate wild Pokémon can be found at, second only to the Level 81-100 Magikarp found by fishing in the Resort Area. As soon as the player steps on to the platform in Diamond or Pearl, the game will automatically initiate the battle.
When the player accesses the Hall of Origin by blowing into the Azure Flute, they are actually no longer on Spear Pillar, rather in a different location; the camera angle changes completely, as does the name of the location (evidenced on the captured Arceus's status screen and in the summary of the player's status on the save screen). Despite this, it is inaccessible by the Surf glitch and tweaking, partly because of the inability to go underground here.
Like Spear Pillar, it is technically outside of a mountain, so the Escape Rope cannot be used to teleport the player back to the entrance of Mt. Coronet. Also like Spear Pillar, it is within range of Mt. Coronet's strong magnetic field, and so Magneton and Nosepass will both evolve here if leveled up.