The Edge of Nothingness is the culmination of the secret Pulsating Worldstone Shard uberquest. In order to get there, players must solve the riddle on the Pulsating Worldstone Shard, then cube it with four Greater Signets of Learning and three Fauztinville Great Runes (one of each type). This will create the Dimensional Key, which provides one charge of the Beyond the Veil skill, which can be used anywhere in Act 5 to open a red portal to the first level of the Edge of Nothingness, an empty corridor except for a one-way red portal leading to the room of the boss Samael, the hardest endgame challenge Median XL has to offer.
The Eternal Conflict between the High Heavens and the Burning Hells has been raging from times immemorial. Angel fighting demon. Demon fighting angel. On, and on, and on... with no end in sight. The demon Lilith captured an angel, Inarius, and to her surprise, she discovered that they both grew tired of the Eternal Conflict. They decided to use the powers of the Worldstone to create Sanctuary, a world apart from the struggles of the everlasting war. They used the Worldstone to hide it from both sides of the conflict, but both sides soon discovered it, and tried to use it to their gain. The Burning Hells invaded Sanctuary, headed by the three Prime Evils, but were faced by a group of heroes, defending their home realm. The prime evils were defeated by mere mortals, but not before Baal could corrupt the Worldstone, trying to bind Sanctuary to the Burning Hells. The archangel Tyrael destroyed the Worldstone to prevent that, but in doing so, he also destroyed what was hiding the Sanctuary from the Heavens, Hell...
...and the worlds beyond the bounds of the known. Then, a foolish hero, in search of glory, to defeat evil, played with the unknown forces of the shards of the destroyed Worldstone, and through the gates of oblivion, from the Edge of Nothingness, stepped in a Herald of the End.