The Source Wall was a massive construct deep in space, with large statues within it. When Darkseid launched an attack on Earth to avenge himself against Superman, Lex Luthor compelled Metron to help him defeat Darkseid. Metron took him to the Source Wall, beyond which lay the one thing which could defeat Darkseid. Metron warned Luthor that only a twelfth level intellect could survive passing through the wall, but Luthor was unconcerned. Luthor did manage to survive his trip through, and found the one thing that could stop Darkseid—the Anti-Life Equation.
In the DC comics, the Source Wall is the barrier between the DC universe and the Source, located at the edge of the Promethean Galaxy. The statues within the Wall are the beings who have tried to unravel the mysteries of the Source, be they conquerors or knowledge seekers. Several cosmic entities in the DC universe have been imprisoned there, including Yuga Khan (father of Darkseid), Ares, and even Darkseid himself. Several beings have managed to pass the Wall and meet the Source, including Batman, Hal Jordan, Barry Allen, and even Metron himself.