Originally posted by S.S.:

The biome you are looking for is the swamp. However, you should defeat the Elder before exploring a swamp, as the boss drops a useful item for it.

Frankly, rather than up the world difficulty, I would explore the swamps first looking for crypts and upgraded food items.

You can upgrade a lot before you go into crypts or beat the Elder. This will make your fight with the Elder easier and you can scope and set up places to go so that when you do beat the Elder you can jump right into the swamp crypts.

Either way you want to check out the swamp biome.