everyone in westeros knows of the grim fate that awaits every man who becomes the lord of harrenhal, but no one is sure why it happened or what started the curse. the only thing certain is that after harren the black, the lords of the castle have been falling victims to a deadly curse.
harrenhalβs curse is like a cancer which infects their host, slowly killing them from within, leading them to a certain death. harrenhal was the first great victory of house targaryen and the garden where the seed of their downfall would be planted.
we know grrm has compared dragons to nuclear weapons and what happens to a place where radioactive material has been dropped? it decays, it kills, it infects, almost like a curse. harrenhal is the chernobyl of westeros.Β
dragons are born from fire and blood magic and that magic haunts the walls of harrenhal. the dragonfire keeps living inside its walls, condemning those who live there to their demise. maybe the same blood magic which doomed valirya is living whitin the walls of harrenhal and that is what caused the curse.
also, alys rivers who used some type of fire magic similar to those of red priests and she lived in harrenhal and danelle lothson was rumoured to mess sith dark magic, specifically blood magic, the same type of blood magic which shiara seastar practiced. all the witches of harrenhal were targaryens who practiced some type of dragon-related magic.