Hell Gates

In Doom II, the demons invade Earth through a portal that the marine finds after defeating the Spider Mastermind. After returning to Earth through this portal, the marine discovers that the planet has been invaded by demons, who have killed billions of people. The only ground spaceport on Earth has been taken over by the demons, who placed a barrier over it, preventing any ships from leaving. The marine battles through hordes of demons and deactivates the force field, allowing the remaining humans to escape. After the survivors escape, the marine is the only human left on the planet. He then receives an off-planet transmission revealing that the demonic base is in the center of his own hometown. He fights through the city until he reaches the base, but sees no way to stop the invasion on that side, so he steps into a portal to try deactivating it from the other side, entering Hell.