The Enter Wormhole mission is available to all starships in any game that was created with the optional Wormhole feature.
When the Enter Wormhole mission is set on a starship, and that starship is at an entry-point for a wormhole, the wormhole will pull the starship in, and transport it to the other end of the wormhole. This consumes no fuel.
Due to the energy flow within a wormhole, starships exiting the wormhole will have their shields down. The next turn, the shields will be back to normal.
If an undamaged starship with the Advanced Cloaking ability traverses a Wormhole, it will emerge cloaked, as long as all cloaking requirements are met. This is due to an unexplained resonance between wormhole energy and advanced cloaking technology.
Wormholes have a stability rating ranging from 1 to 100. More stable wormholes are generally safe to travel, but as the wormhole becomes more unstable and heads towards collapse, it can become quite dangerous. As the stability decreases, the risk of a starship taking damage and the amount of damage it receives increases, and highly unstable wormholes are capable of destroying small and medium starships.
See also: Out of Fuel.