Did you know that HP Lovecraft was neither claustrophobic nor agoraphobic but rather some strange mixture of the two? He was terrified of large enclosed spaces*. This makes so much sense if you've read enough Lovecraft. Seriously horrible things happen to people all the time as soon as they find a yawning dark cavern that is seemingly infinitely vast.
I learned this from reading The Roots of Horror in the Fiction of H.P. Lovecraft by Barton Levi St. Armand.
*And not just caves because that's only ordinary speluncaphobia.
