The Realm of the Valg is the currently nameless homeland of the demonic antagonists within the Throne of Glass series, known as the Valg. The realm is home to many significant Valg residents, most noticeably Maeve, one of the primary villains in the series.
Many tens of millenia ago, the realm where the Valg originated from was full of wars, suffering and destruction to a large extent. A might war was waged against the three Valg Kings (Orcus, Mantyx and Erawan) against whatever forces that ceased true ownership of their land. As the three Kings became victorious, they turned their realm into one of eternal darkness, cold, ice and wind. This was considered a paradise for the Valg demons.
The next thousand years or so, the Valg Kings ruled equally and balanced in power. They created a world where they could finally reign in peace. The Valg Kings bred their royalty through numerous bloodlines, producing Valg offspring (princesses and princes) to ensure their land would remain unconquered by any foes and remain in their ownership only. These kings ruled in peace until Maeve, the Dark Valg Queen with tremendous dark power, came within their vicinity. Maeve beared gifts to the kings, who were flattered by the gesture and admired the queen for her cruelty, power and beauty. Maeve only had her eyes open for one king in particular, however.
Queen Maeve married King Orcus, the oldest and strongest Valg King. But it was not enough for her: she was not content. She was restless to leave, to witness and conquer foreign realms, and to rule unchallenged. She yearned to search and seek out multiple realms, if only to claim them as her own for possession of power. So she used her gifts to look through the world, at tears between it, separating realms: Wyrdgates. By piercing the veil, the Wyrdgate separating the Valg realm and another realm, she saw Erilea, a world full of light, green and singing. So Maeve waited in the Valg Realm for an opportunity to leave.