Microverse

Microverses are dimensions occurring within the fictional Marvel Universe. The Microverses are often visited by the Fantastic Four in various adventures. They were formerly defined as any universe only accessible through vibrational attunement (shrinking). The belief that these worlds exist "within" atoms may have given rise to the stock phrase "There are worlds within worlds". It is not actually the microverses that are microscopic in size but rather the nexuses which make them accessible. It is thus theoretically possible to enter the same microverse from different points on Earth. The volume of these microverses are contained within spacewalls which can only be breached at certain points. It is these breaches that create accessible portals.