I was recently having a discussion with another user about whether or not the Doom of Valyria could have had a hand in the odd season lengths that occur in Westeros. Their point was that following large scale volcanic activity a long winter could occur due to all the extra debris in the sky. For more information see Nuclear Winter. I told the user it appears there isn't much evidence as too what happened to Valyria and the surrounding lands following the Doom. However, I'm not sure where Valyria is on Planetos and if it the effects of the Doom could even impact Westeros.
So that leads to the question where is Valyria?