The Odyssey by Homer is the story of Odysseus' struggles to return home from the Trojan War. There are many obstacles making his return difficult, especially the enmity of the god Poseidon. 

One major obstacle Odysseus encounters is the goddess or nymph Circe who traps the sailors and turns them in to swine using magical potions.

The nymph Calypso traps Odysseus on her island for seven years because she wishes to make him her husband, and thus prevents him from returning to Penelope.

The Sirens are evil women who lure sailors to death with their enticing songs.

The Cyclops Polyphemus traps Odysseus and his men in a cave, and uses some of the sailors for food.

Scylla and Charybdis are sea monsters that Odysseus and his sailors must avoid. 

The Laestrygonians are cannibalistic giants who eat some of Odysseus' sailors.