Harry Potter and the Half-Blood Prince

“It has known magic,” said Dumbledore simply. Harry could not tell whether the shivers he was experiencing were due to his spine-deep coldness or to the same awareness of enchantments. He watched as Dumbledore continued to revolve on the spot, evidently concentrating on things Harry could not see.

“This is merely the antechamber, the entrance hall,” said Dumbledore after a moment or two. “We need to penetrate the inner place… Now it is Lord Voldemort’s obstacles that stand in our way, rather than those nature made…”

Dumbledore approached the wall of the cave and caressed it with his blackened fingertips, murmuring words in a strange tongue that Harry did not understand. Twice Dumbledore walked right around the cave, touching as much of the rough rock as he could, occasionally pausing, running his fingers backward and forward over a particular spot, until finally he stopped, his hand pressed flat against the wall.

“Here,” he said. “We go on through here. The entrance is concealed.”

Harry did not ask how Dumbledore knew. He had never seen a wizard work things out like this, simply by looking and touching; but Harry had long since learned that bangs and smoke were more often the marks of ineptitude than expertise.

Dumbledore stepped back from the cave wall and pointed his wand at the rock. For a moment, an arched outline appeared there, blazing white as though there was a powerful light behind the crack.

“You’ve d-done it!” said Harry through chattering teeth, but before the words had left his lips the outline had gone, leaving the rock as bare and solid as ever. Dumbledore looked around.

“Harry, I’m so sorry, I forgot,” he said; he now pointed his wand at Harry and at once, Harry’s clothes were as warm and dry as if they had been hanging in front of a blazing fire.

“Thank you,” said Harry gratefully, but Dumbledore had already turned his attention back to the solid cave wall. He did not try any more magic, but simply stood there staring at it intently, as though something extremely interesting was written on it. Harry stayed quite still; he did not want to break Dumbledore’s concentration.

Then, after two solid minutes, Dumbledore said quietly, “Oh, surely not. So crude.”

“What is it, Professor?”

“I rather think,” said Dumbledore, putting his uninjured hand inside his robes and drawing out a short silver knife of the kind Harry used to chop potion ingredients, “that we are required to make payment to pass.”

“Payment?” said Harry. “You’ve got to give the door something?”

“Yes,” said Dumbledore. “Blood, if I am not much mistaken.”

“Blood?”

“I said it was crude,” said Dumbledore, who sounded disdainful, even disappointed, as though Voldemort had fallen short of higher standards Dumbledore expected. “The idea, as I am sure you will have gathered, is that your enemy must weaken him– or herself to enter. Once again, Lord Voldemort fails to grasp that there are much more terrible things than physical injury.”

“Yeah, but still, if you can avoid it…” said Harry, who had experienced enough pain not to be keen for more.

“Sometimes, however, it is unavoidable,” said Dumbledore, shaking back the sleeve of his robes and exposing the forearm of his injured hand.

“Professor!” protested Harry, hurrying forward as Dumbledore raised his knife. “I’ll do it, I’m—”

He did not know what he was going to say—younger, fitter? But Dumbledore merely smiled. There was a flash of silver, and a spurt of scarlet; the rock face was peppered with dark, glistening drops.

“You are very kind, Harry,” said Dumbledore, now passing the tip of his wand over the deep cut he had made in his own arm, so that it healed instantly, just as Snape had healed Malfoy’s wound, “But your blood is worth more than mine. Ah, that seems to have done the trick, doesn’t it?”

The blazing silver outline of an arch had appeared in the wall once more, and this time it did not fade away: The blood-spattered rock within it simply vanished, leaving an opening into what seemed total darkness.

“After me, I think,” said Dumbledore, and he walked through the archway with Harry on his heels, lighting his own wand hastily as he went.

An eerie sight met their eyes: They were standing on the edge of a great black lake, so vast that Harry could not make out the distant banks, in a cavern so high that the ceiling too was out of sight. A misty greenish light shone far away in what looked like the middle of the lake; it was reflected in the completely still water below. The greenish glow and the light from the two wands were the only things that broke the otherwise velvety blackness, though their rays did not penetrate as far as Harry would have expected. The darkness was somehow denser than normal darkness.

“Let us walk,” said Dumbledore quietly. “Be very careful not to step into the water. Stay close to me.”