The God’s Eye is the huge lake in the Riverlands , south of the Trident and west of the kingsroad in Westeros. Harrenhal sits on its north shore, and the Isle of Faces is in the middle of the lake.

In Game of Thrones terms

It’s the place tied to the “Battle Above the Gods Eye,” a famous event from the lore around House Targaryen. The name comes from the lake’s shape on a map, with the Isle of Faces acting like the “pupil”.

Quick location clue

If you picture the map of Westeros, look for:

  • The Riverlands
  • Harrenhal
  • The Isle of Faces in the center of the lake

In plain English: it’s not a city or castle, but the biggest lake in the center-south of Westeros.

TL;DR: The God’s Eye is the largest lake in Westeros, in the Riverlands, with Harrenhal on its north shore and the Isle of Faces in the middle.