"The closet is in the wall."
Translation:벽장은 벽에 있어요.
벽장이 벽 안에 있어요 this makes more sense cuz the closest is.....IN the wall..?
Yeah that would be ok too. As it turns out there are a lot of prepositions, or rather postpositions in Korean that are rather similar. In such a manner, 속에 should be allowed aswell, but 에 works just fine.