Somewhere between Althrea and Neyta, there was an eternal dungeon that belonged to Trinity.
It was an underground terrain with a complex cave system that took Trinity a whole year to map out completely. As if to reward the explorers, the commodities coming out of this dungeon were magic stones; from mana stones to aetherite. As of now, only twenty percent of the dungeon's terrain had been mined, and by the time they reached the farthest tunnel, the early ones would already regenerate more stones.
Naturally, it was considered as Trinity's most precious dungeon. What they didn't know was that the dungeon became precious not only because of the resources it brought but also because of its resilience. The terrain itself was made to absorb magic and vibration, so no matter what they did while mining, there was no fear of the cave system collapsing.
Which means, it was perfect for espers to go wild with their skills.
