" The Valyrians were more than dragonlords. They practiced blood magic and other dark arts as well, delving deep into the earth for secrets best left buried and twisting the flesh of beasts and men to fashion monstrous and unnatural chimeras. For there sins the gods in their wroth struck them down.
Valyria is accursed, all men agree, and even the boldest sailor steers well clear of its smoking bones... but we would be mistaken to believe that nothing lives there now. "

― George R.R. Martin , Fire & Blood (A Targaryen History, #1)