From Diablo Wiki
Aranoch is a desert region in central Sanctuary, the Diablo world. Diablo II’s Act II takes place in its only major city, Lut Gholein, and the surrounding areas. Furthermore, Aranoch plays a noticeable role in the history of Sanctuary, particularly during the Dark Exile.
The following text from the Diablo II game manual describes the land of Aranoch in general terms:
“The Tamoe mountain range, which lines the eastern border of the Western Kingdoms, acts as a natural barrier into these provinces. Although impassable in most areas, these mountains hold a vast and lush woodlands. These forests stand in stark contrast to the bleak wastelands lying beyond them to the east: the flat, unforgiving, sand-swept deserts of Aranoch.
Boasting one of the harshest climates in the world, the deserts of Aranoch claim the lives of many each year. Only the most robust and highly-trained nomads survive longer than a few hours in this scorching environment. This vast desert land is mainly comprised of vast, empty tracts, punctuated with but a few specially-adapted plants and trees. Water is a rarity among the sand dunes of Aranoch, with dry spells reportedly lasting for years. The climate of this desert ranges from life-threatening heat during summer days, to dry frigid winds during winter nights.
Set on the western edge of the Twin Seas, the jewel city of Lut Gholein has actually prospered in the merciless environment of Aranoch. Most credit this to the city's coastal location and strong sea trading ties with the kingdoms to the east and west. Although a few bands of nomadic people have found ways to survive in this hostile desert, most steer clear of these sandy wastelands.
The perilous nature of Aranoch's unique and deadly environment is without equal. Few creatures could survive in habitats so unforgiving, but some hardy beasts have managed. Now twisted by the chaos brought about by the arrival of the Prime Evils, these unique beasts are fearsomely powerful.”
One interesting detail is that, in the Diablo manual, Aranoch is referred to only as “the East,” and it appears to have story elements that were later shifted to Kehjistan. For example, the Diablo manual states that both Baal and Mephisto “were then buried beneath the dunes of the desolate Eastern Sands,” whereas in Diablo II, Mephisto is said to have always been held in the temples of Travincal, in Kurast.
Known as the Jewel City of the Desert, Lut Gholein is a major city and port on the shores of the Twin Seas. During the Dark Exile, the Horadrim ambushed Baal just outside the city and defeated him; however, Baal’s Soulstone was damaged in the battle, leading to the entombment of the Lord of Destruction with Tal Rasha in the deep desert. In Diablo II, the player must hunt for the location of the tomb before Diablo can find it and free Baal.