Menalaus is not a place, but a person, specifically, the king of Sparta. He and his wife, Helen, there. They host Odysseus’ son, Telemachus, for dinner and Menalaus, not yet aware that Telemachus is the son of Odysseus, tells the younger man about the great warrior Odysseus, who is missing and presumed dead, a casualty of the Trojan War. This event occurs in Book IV of The Odyssey:
“Menalaus entertained his guests very hospitably, and overhearing Telemachus call his friend’s attention to the splendor of the house, he explained to them how much toil and sorrow he hand endured, especially through the murder of his brother, Agamemnon, the plundering of his house by Paris when he carried off Helen, and the death of so many of his brave comrades at Troy. ‘There is one man, however,’ he added, ‘of whom I cannot even think without loathing both food and sleep. I mean Odysseus’.”
After surmising that Telemachus is Odysseus’ son, Menalaus tells him about Odysseus’s disappearance, and about his own experiences returning from the Trojan War and his encounter in Egypt with Proteus, who transforms into different life forms, for example, dangerous animals, or into water or fire as the circumstances dictate, but whom, if captured in human form, could be compelled to answer questions regarding mysteries like how Menalaus could return home and, as importantly about the fate of Odysseus:
“He [Proteus] told me also of the fate of Ajax, son of Oileus, and of my brother Agamemnon. Lastly, he told me about Odysseus, who he said was in the island of the nympth Calypso, unable to get away inasmuch as he had neither ship nor crew.” [In The Odyssey, Calypso detains Odysseus for seven years.]
Helen, of course, is at the center of the Trojan War, having been taken, as mentioned, by Paris for his own. Menalaus and Helen would spend the evening telling Telemachus a great deal about Troy and the Trojan Horse. Telemachus departs Menalaus’s home and continues his journey.
When Telemachus sets out for information of his father's whereabouts, he meets Menelaus, who is home in Sparta. Their exchange is recounted in Book 4, "The Red-Haired King and His Lady."
Menelaus travels from Troy back to his home in Sparta, where, according to the character sketch on eNotes, he spends the duration of The Odyssey being "the happy husband and father, the good ruler, and the perfect host."