Hy-Brasil is a mysterious island appearing on maps from 1325 to the 1800s. In Irish myth, it was said to be clouded in mist except for one day every seven years, when it became visible but still could not be reached. Stories about the island have circulated throughout Europe for centuries, with tales that it was the promised land of saints or a paradise where an advanced civilization lived.
On most maps, the island was located roughly 321 km (200 miles) off the west coast of Ireland in the North Atlantic Ocean. One of the most distinctive geographical features of Hy-Brasil on those maps is that it often appears as a circle with a channel (or river) running east to west across it.
Hy-Brasil on a map from 1325. (Ocultoreveladoaverdade)