The Photon Dungeon is an underground dungeon area. While it is not anything noteworthy, normally, it's a good place to grind for levels.
This was the site of the infinite spawning Black Werewolf monsters, a special monster that was set to be released in a future update. Team Triple Threat were able to stop the infinite spawning by laying the corpses of the monsters on the spawn point, but were unaware that was the solution. Instead they were drunk off the battle, killing one Werewolf after another. Because the Black Werewolves were of mid-boss level of strength and yet killed so easily, it served as a testament to how powerful Triple Threat really is.
System debugger, Myuria, arrived with her sunbae (Korean word for senior/upperclassman) to fix the issue as it was caused by the server being unstable in preparation for the upcoming expansion update.