Anchor I discovered I had claustrophobia in student backpack days when I went in a supposed underground city in Cappadocia in Turkey, in reality mile after mile of caves and tunnels where Christians hid out to avoid persecution hundreds of years ago. It was a really overwhelming feeling, verging on panic and I had to get out quickly.
I had it again years later at Cu Chi in Vietnam where I daftly went through a bit of the tunnel system the Viet Cong had built. Horrible feeling. Of all the hobbies in the world caving and potholing are the ones that baffle me.