Aside from the super-obvious, like Asshai & Valyria, what are other locales you think might be, or definitely are, thin places like you call Harrenhal? What evidence or signs would definitively indicate such? Would that weird black stone be one, meaning maybe Pyke & Oldtown are? What about places with possible magic defenses, like Winterfell, the Wall or Storm’s End? Does their long-term magic make a thin place, or does being a thin place make the magic possible?

There’ a lot of places which could qualify: Asshai; maybe High Heart; Chroyane definitely is one, given what’s going on with time and space in that vicinity; the Night Fort is a good contender; the Twins might become one although I think it might need to marinade a bit longer.

However, I think other places don’t fall into that category. We have other terms, like “hinge of the world” for places of power – thin places would be a subset which are places that are concentrations of human suffering as well. Winterfell doesn’t count – it’s clearly a place where human life is protected – and I think Storm’s End, etc. are in that same category, although less important to the narrative.