Dean thinks it might be a side-affect of Falling–that after losing the hugeness of a Grace, there’s too much experience and knowledge to keep it all bottled up.
Well, that, and humans generally like to tell stories.
So Dean listens. And in the early hours of the morning, when he closes his eyes after a roll in the hay, Castiel paints the night sky of the Sahara desert across his eyelids, speaking lowly of the cold and heat and the people who live there.
Cas talks about Spain, and Paris, and Pangaea. About Australia before it was Australia. About Chile. Lebanon. Malawi.
“What’s your favorite place?” Dean asks one night.