Originally posted by marcusaddamsson:

Generally speaking, a biome's area needs to be a certain size so that a Dungeon/Village/etc can appear. I had this same issue with my first first seed. Anyway, my point is.. try to find an area that has lotsa lotsa swamps, not just bits and pieces... you'll find a Dungeon.

I use to believe that too. But recently found a rather large swamp that only had 1 crypt, but then found a tiny strip elsewhere that had 3 crypts.