The Black Hole was Jagex's early punishment in RuneScape Classic, before Jagex implemented the banning system. Players who misbehaved were sent to the Black Hole as punishment for their actions, and they would remain there for an undefined amount of time before being removed. The Black Hole was implemented in 2001 and later removed from RuneScape Classic on December 2001 in RuneScape.
Players are able to visit The Black Hole by selecting the Activate option the Disk of returning in the Dwarven Mines beneath Falador. In here, players will encounter Thordur, but will not be able to move around.
Players can visit a blacker blackhole by selecting the Blackout option, which takes players to a completely dark area where players are freely able to move around, allowing screenshots to be easily taken without background disruption. Players in the blacker blackhole can leave using the light found in the south-west corner. Players who attempt to leave both black holes will be warned that any items left on the ground will disappear permanently.
Note: You can still get out of the main black hole where Thordur resides even if you do not have the disk of returning in your inventory.
Upon the official release of Thordur's Black Hole in 2001, some players deliberately misbehaved and violated the Code of Conduct for the sole purpose of seeing what the Black Hole was like. As a result of this, Andrew Gower made the decision to program a clone of the Black Hole, so that any player could visit the area without breaking any rules. Those wishing to enter would visit Thordur in the western side of the Dwarven Mine under Falador, who would sell them a disk of returning for 10 coins. Once the player obtained the Disk, they were then able to climb down a nearby ladder to access the cloned Black Hole and would use the disk of returning to get out.
The Black Hole and its clone were then removed from the game in December 2001 because of a scam where players would ask one another to drop the disk of returning, thus causing them to be stuck in the black hole until a member of Jagex staff removed them.
Although it has now been removed from RuneScape 3, players are still able to visit the Black Hole on Old School RuneScape after the release of the disk of returning in 2013. Players wishing to enter the hole simply have to activate the disk of returning in the Dwarven Mine to be teleported directly into the Black Hole, where they will meet Thordur.