From Bulbapedia, the community-driven Pokémon encyclopedia.
Fogbound Lake is situated high above Foggy Forest and accessed after going through Steam Cave. It can be seen after the battle with the fake Groudon. One Time Gear is placed in the center of the lake with Uxie guarding over it. Fogbound Lake is located on top of a pillar with waterfalls flowing over the edges into lakes underneath. It is filled with many Illumise and Volbeat, which glow at night. Prior to the Guild's expedition, Uxie had protected the location of the lake by erasing the memories of explorers.