I was going to say "not very many", but then I thought about it. A hidden shrine under the city, a cave where a pirate treasure is hidden, a sunken temple dedicated to a forgotten god, and most recently a long voyage into a vast system of natural caverns. I guess all of those could count as 'dungeons', even if they're not really the 'enter here for 10'x10' stone corridors stocked by mad wizard' type.
Still, most of the action in my game has been above ground, in cities or the wilderness.
J