Great Portal (Earth-6531)

"That looks like a collapsing neutron star inside of an Einstein-Rosen bridge!"

- - Bruce Banner

The Great Portal is a lone wormhole at the seas of Sakaar.

History
The Great Portal formed millions of years in the past at the atmosphere of Sakaar. This made the planet a source of lost ships and individuals who got lost in space. The Grandmaster used this to enslave the confused crash-landing extraterrestrials to serve as slaves and gladiators for his Contest of Champions at his his arena.

After the death of Odin on Norway, Earth, Hela's seal was finally broken, enabling her to escape her banishment on Hel. Upon arriving on Earth, she battled Thor and Loki, who attempted to escape in the Bifrost. However, she followed them, and threw the siblings out of it, and they eventually fell through the Great Portal.

As Thor became stranded in the planet and forced to compete as a gladiator, he, Loki, the Hulk and Vallkyrie devised a plan to escape Sakaar using the Great Portal. After Thor was telepatically contacted by Heimdall, the All-Seeing Asgardian guided him to escape through the portal, which they were able to do.