Dimensional Doors are a form of technology usable by all races, which opens up a portal to another location, another dimension, or another universe (in the case of very large portals). They run on magical energies, and thus are built where those energies run high. They tend to be in the shape of a circle, and are always at last five meters wide.
There is a slight risk to Dimension Doors. If they are overloaded (too any people or items going through at once), they have a nasty tendency to teleport the people to some hostile realm, often near a volcano, under water, or other similar places. Some reports indicate families have been teleported up to space by accident. Other cases show them vanishing to some strange realm.