Great Barrier

The Great Barrier is an immense energy field surrounding the galactic core. It was created 500,000 years ago by the Q Continuum to imprison The One for its crimes. (TNG novel: Q-Strike)

In 2287, Sybok (having been influenced by The One) commandeered the USS Enterprise-A and succesfully took it through the Great Barrier in search of Sha Ka Ree. (Star Trek V: The Final Frontier)