You're interested in the book "El mundo de hielo y fuego" (The World of Ice & Fire)!
If you're looking for free resources related to The World of Ice & Fire, you might consider:
: Author George R. R. Martin has officially released specific chapters as previews. These include: Aegon's Conquest : Available as a sample on the official website The Ten Thousand Ships : A detailed history of Nymeria’s voyage. The Westerlands : Released as an additional excerpt. Official Companion App A World of Ice and Fire