The Smoking Sea

Where the Valyrian peninsula once stood, only a smoking sea remains, born the day the land sank and the water swallowed it whole. Volcanoes still burn beneath the surface, and in some stretches the water is said to boil.

No sensible sailor sails into it: it is said to be infested with krakens and haunted by demons. Gerion Lannister vanished there while searching for Brightroar, his House's ancestral sword, and nothing more was ever heard of him or his crew.

By his own account in A Feast for Crows, Euron Greyjoy sailed across the Smoking Sea and glimpsed Valyria with his own eyes. He boasts of being the only sailor to have entered those waters and come back alive to tell of it.

Lord Rodrik Harlaw hears the tale and doesn't buy it: to him it sounds more like boasting than a real feat.

In A Dance with Dragons, in Meereen, Daenerys Targaryen studies an old tapestry given to her by Xaro Xhoan Daxos, woven before the Doom of Valyria. It shows no sea where the water now boils: Valyria still sits joined to the mainland, not yet an island.

Aboard the Selaesori Qhoran, Tyrion Lannister recalls that his uncle Gerion bought slaves to fill out the crew of the ship with which he meant to cross the Smoking Sea, after half the original crew deserted before it ever set sail.

Victarion Greyjoy, for his part, counts among his brother Euron's feats having sailed those waters and come back alive to boast of it.