The cavern.
After all the Inferi had been brought under control, the electricity in the lake gradually dissipated. Once they had made sure there were no other creatures in the water, they crossed the lake and reached the Island in the Middle of the Lake.
Once they stepped onto the Island in the Middle of the Lake, they saw an eerie blue glow coming from a stone basin resembling a Pensieve, with a pedestal beneath it, like a lamp.
They stood side by side before the stone basin and looked inside. It was filled to the brim with emerald-green liquid that gave off a shimmering phosphorescence.
At that moment, Kreacher plunged into the lake again, feeling his way toward the place he remembered.
As for whether Regulus might have become an Inferius, none of them were worried in the slightest. Inferi had to be summoned and controlled by a Dark Wizard using Dark Magic, and Regulus clearly had not met that condition.
Just as Kreacher entered the water, Sirius jumped in after him, but he resurfaced less than a minute later.
"Lumos doesn't work down there. There seems to be some kind of force in the lake that restricts it."
Douglas casually snapped his fingers. A stream of clear water appeared out of thin air and flowed toward the ground, but just as it approached the ground, it suddenly vanished into thin air again.
"It's not just the lake. Some restrictions have been placed on the Island in the Middle of the Lake too. For instance, you can't drink water here. As for the measures in the lake, I think most of them were meant for the Inferi. Voldemort needed to give them a suitable environment to survive in. And for magic to last this long without being destroyed by