re: Crackpot ASOIAF Theories SPOILERS

The Fourteen Fires is an immense chain of volcanoes extending across the neck of the Valyrian peninsula.

"The Valyrians sheep-herding folk of the Valyrian peninsula, discovered dragons lairing in the Fourteen Fires, leading to their rise to power. Later the Valyrians sent their slaves to mines in the Fourteen Fires, searching for gold among other things. Sometimes firewyrms were encountered in the shafts of the mines by the slaves, leaving only corpses.

Great heat emanates from dragons' bodies, to the point that they steam during cold nights. They breathe extremely hot fire and cook their meat before eating it."

So GRRM can go either way with this one.

Winterfell is where the last battle at the war of dawn was fought(The place where winter fell). When it was the done, the last hero(also Bran The Builder) sealed his weapon - Lightbringer, actually a dragon, building a castle over it. He knew a day will come when the others will rise again so when the castle was destroyed Lightbringer was set loose into the north.

Or...

Given the volcanic nature of the destruction of Hardhome, The hot springs under Winterfell could just be a result of nearby volcanic activity. This doesn't mean there isn't anything significant under Winterfell, but that it probably isn't dragons