From A Wiki of Ice and Fire
The Smoking Sea is the place where the sea flooded into the shattered remnant of the Valyrian peninsula after the Doom of Valyria. Filled with volcanoes and smoking stacks of rock, it is said to boil in places and to be haunted by demons.
According to semi-canon sources it was once only a strait, but with the Doom of Valyria, the peninsula was subsumed and the strait was enlarged becoming the Smoking Sea. It remains a dangerous area to sail and the waters are reported to be infested with krakens.
Circa 292AC, Gerion Lannister went on a quest to find the ancestral sword Brightroar and any other treasures that might have survived the Doom of Valyria. Almost a decade passed after his ship the Laughing Lion left Lannisport but Gerion never returned. Lord Tywin Lannister sent men to look for his lost brother and they traced him as far as Volantis, where half his crew had deserted him because of his intent to sail into the Smoking Sea. He was forced to buy slaves to replace them. 
A Feast for Crows
References and Notes
- ↑ 1.0 1.1 A World of Ice and Fire
- ↑ A Game of Thrones RPG and Resource Book, Guardians of Order
- ↑ A Storm of Swords, Chapter 8, Daenerys.
- ↑ A Dance with Dragons, Chapter 33, Tyrion, states he was eighteen when Gerion left.
- ↑ A Dance with Dragons, Chapter 8, Tyrion.
- ↑ A Feast for Crows, Chapter 29, The Reaver.