The three of them descended the steps, with Dumbledore leading and Harry in the middle.
Will brought up the rear, studying the rock walls as he walked, until they entered the seawater. It was cold enough to cut to the bone, but the Bubble-Head Charm shielded them from the chill and let them breathe freely.
Dumbledore swam ahead, the light from his wand tracing a bright path through the darkness.
They passed through a black fissure in the rock beneath the water. After a while, it narrowed into a pitch-dark passage, its slime-coated walls barely three feet apart.
Will frowned and did his best not to touch the muck.
After roughly fifteen minutes, the passage began to slope upward, and they entered a cave.
It was enormous, far larger than Will had expected. Their wandlight illuminated only a small patch around them; beyond it lay darkness too thick to penetrate.
The air reeked of decay mingled with the salty stench of the sea.
Dumbledore stood still and slowly turned, sweeping his wandlight around the cave. He moved as though he were sensing something.
"Tom placed a great deal of magic here," he said softly. "I can feel it. This is only an antechamber. The real entrance is hidden."
Will examined the magical structures around them. He knew exactly what was there. His gaze swept over the walls and ceiling before settling on an unremarkable corner.
A magical structure stood out clearly there.
Dumbledore seemed to notice it too. He stopped before that section of wall and pressed his palm flat against it.
"Here," he said.
He tapped it with his wand. Dazzling white light shot from the rock, outlining an archway, but after only a few seconds, the light vanished and the rock returned to normal.
Dumbledore frowned slightly.
"It