You said it was twenty feet!” “Yeah. You’ll have to trust…

““You said it was twenty feet!” “Yeah. You’ll have to trust me. Put your arms around my neck and hang on.” “How can you possibly—” “There!” cried a voice behind them. “Kill the ungrateful tourists!” The children of Nyx had found them. Annabeth wrapped her arms around Percy’s neck. “Go!” With her eyes closed, she could only guess how he managed it. Maybe he used the force of the river somehow. Maybe he was just scared out of his mind and charged with adrenaline. Percy leaped with more strength than she would have thought possible. They sailed through the air as the river churned and wailed below them, splashing Annabeth’s bare ankles with stinging brine. Then—CLUMP. They were on solid ground again. “You can open your eyes,” Percy said, breathing hard. “But you won’t like what you see.” Annabeth blinked. After the darkness of Nyx, even the dim red glow of Tartarus seemed blinding. Before them stretched a valley big enough to fit the San Francisco Bay. The booming noise came from the entire landscape, as if thunder were echoing from beneath the ground. Under poisonous clouds, the rolling terrain glistened purple with dark red and blue scar lines. “It looks like…” Annabeth fought down her revulsion. “Like a giant heart.” “The heart of Tartarus,” Percy murmured. The center of the valley was covered with a fine black fuzz of peppery dots. They were so far away, it took Annabeth a moment to realize she was looking at an army—thousands, maybe tens of thousands of monsters, gathered around a central pinpoint of darkness. It was too far to see any details, but Annabeth had no doubt what the pinpoint was. Even from the edge of the valley, Annabeth could feel its power tugging at her soul. “The Doors of Death.””

— Rick Riordan