Rogue Galaxy Quarry: The Fallen Monarch
The closest save teleporter to teleport to in order to reach The Fallen Monarch is Ti'atha Forest - Midpoint. Once you teleport in here you'll want to head back towards where I am on the map, where the shop is location by the large waterfall. This is where the location to summon the boss is.
The item required to summon this boss is a sword called Alexander which can only be made through the factory in Rogue Galaxy. That is also where I officially say screw this and stop writing the Quarry guide. The factory system in this game interests me null so I will post the location for him but he is the last Quarry I am going to cover. Anything that comes after him, sorry, you're on your own if you want to go through the shit show of learning how the factory works.
Here is a Factory Guide on how to make Alexander via Rogue Galaxy wiki