Here's why this is considered the climax:
* Rising Tension: The entire book builds up to this confrontation. Percy, Annabeth, and Tyson are on a quest to find the Golden Fleece, which is the only way to save Camp Half-Blood from the destruction caused by the Titan, Kronos. They face many challenges and dangers along the way, but the threat of Polyphemus looms large.
* Final Showdown: The fight against Polyphemus is the ultimate test of their courage, strength, and ingenuity. The Cyclops is a powerful and brutal creature, and Percy and his friends must use all their skills to survive.
* Resolution of the Central Conflict: The outcome of this battle determines the fate of Camp Half-Blood and, ultimately, the fate of the world. If Percy fails, the Titans will be released and the world will be plunged into chaos.
However, the book doesn't end with the fight against Polyphemus. It's a crucial point, but the climax isn't fully resolved until Percy and his friends successfully retrieve the Golden Fleece and save Camp Half-Blood. This is when the tension and conflict fully resolve, marking the true end of the book.