Here is a vague description of a story I'm trying to identify:
In the story, there is some sort of a support group for people who have glimpsed, through doors or cracks in walls, other worlds and/or other dimensions. At least one person tells a story about looking through a crack(?) and seeing a world with an unearthly sky and strange trees. I believe that the title of the story includes the phrase "Layers of An Onion" or "Skin of An Onion."
This is the best I can do.