Sea of Monsters

The Sea of Monsters is a sea in which monsters like Polyphemus, Scylla, the Sirens, and other monsters and godly things like Circe, the sorceress, live in. Much like Olympus and the Underworld, the Sea tends to move around following the light of the Western World. It was originally in the Mediterranean Sea in the ancient times. Because of its triangular size, the Mist hasn't been able to hide it completely and the area has become infamous among mortals because of the planes and ships that disappear there. The Sea of Monsters is known to mortals as the Bermuda Triangle.

Entrance
There are only two known entrances to the Sea of Monsters which were both used by heroes on quests. There are the Clashing Rocks which were used by the original Jason, when he was on his quest with the Argonauts. They roll past each other so quickly it's nearly impossible to get through them (hence the name "Clashing Rocks"). Jason and the Argonauts only survived because of the protection from Hera.

The second is the strait of Scylla and Charybdis which was used by Clarisse, daughter of Ares, Percy, son of Poseidon, Annabeth, daughter of Athena, Tyson, Cyclops son of Poseidon, and the skeleton crew on The Quest for the Golden Fleece in The Sea of Monsters while on the CSS Birmingham, an old Confederate warship given to Clarisse by her father, Ares.

Circe's Island
The island is rather beautiful and seems like a tropical paradise with a five star resort on it. But appearances can be quite deceiving. Females are in no real danger and will be treated quite well by Circe and her staff. Circe has a strong hatred of men. The only improvement is that she doesn't turn men into pigs any more, but guinea pigs because they are much easier to clean. She trapped Edward Teach, a.k.a. Blackbeard, son of Ares, there sometime earlier. She also trapped Percy when he and Annabeth were shipwrecked on her island after the abrupt sinking of the CSS Birmingham by Charybdis. However, Annabeth rescued him by eating one of Hermes' chewable multivitamins and attacking Circe with her bronze knife so that she could get the sorceress to open the lid of the guinea pig cage. Annabeth and Percy both escaped her while the sorceress was attacked by Blackbeard and his pirate crew, who had been turned into guinea pigs 300 years ago.

Sirens' Island
This Island perhaps fits the best description of a monster's island. The Sirens' Island is barren, dank, and littered with wrecks and bones of the victims of the Sirens. Despite this, it is considered a profound experience to hear the song of the Sirens, because it can tell you things about yourself that even you didn't know and you can become a lot wiser if you survive the experience.

Polyphemus' Island
By far the most beautiful island in the Sea of Monsters, though this is thanks to the work of the Golden Fleece which has enhanced the beauty of the plants and animals of the island there. For example, the sheep there are the size of a hippopotamus. This is the island of the carnivorous satyr-loving eater Cyclops (and son of Poseidon) Polyphemus whom Percy, Grover, Clarisse, Tyson, and Annabeth fought so that they could retrieve the Golden Fleece from his island to heal Thalia's tree at Camp Half-blood in Long Island, New York City.

Hephaestus' Forge
Hephaestus has a forge near/in the Sea of Monsters in the form of a volcano.