The Dimension

The Dimension is a portal opened by dimensional scissors (and on rare occasions, exceptionally powerful magic users) that allows the user to travel to another dimension. The portal's appearance can vary depending on the destination.

Appearance
It is a huge tunnel of the portal dimension.

Trivia

 * A portal in science fiction and fantasy is a technological or magical doorway that connects two distant locations separated by spacetime. It usually consists of two or more gateways, with an object entering one gateway leaving via the other instantaneously. There are numerous worlds throughout the galaxy (and beyond). It dials one another if it has the destination address, and offers practically instantaneous access to all larger moving bodies without permitting atmospheric exchange, and another type of portal.