Door 2: Wall Passage, Pembroke Castle, Pembrokeshire, Wales, the UK.
Henry VIII (yup, that one) spent his childhood here. It's a big, worn, drafty old place, with an enormous cave in the lower levels that dates back to prehistoric times. Pembroke is a tiny town that basically has this huge castle, its huge moat (actually a millpond that extends into a small lake, which proceeds to run into a river that goes 97 miles to the sea), and the ruins of a mill that's older than the castle.
I remember it because this is the first holiday I was ever on which I planned, organised and paid for all by myself. It's also the only holiday I've ever been on by myself. I stayed in an old coaching inn and walked round and round the castle and millpond for three days and felt boring and happy and utterly relaxed. I met a couple of Filipino caregivers, which strengthens my belief that we have infiltrated every level of service everywhere.
I also got catcalled by a car full of redheaded boys. Is this a thing that happens a lot in Wales?