The Tomb of Tal Rasha is the last "resting" place of Tal Rasha used to hold not only its namesake, but also the essence of Baal inside the broken Soulstone lodged inside Tal Rasha. The tomb was made as one of seven identical tombs in the Canyon of the Magi.
Contents
Background
After Baal finally had been captured by the Horadrim, the Soulstone provided by Archangel Tyrael had been shattered. Knowing there was no other way to permanently capture Baal, the Horadrim's powerful leader, Tal Rasha offered to lodge the stone in his own flesh to forever wrestle the spirit of Baal.
With heavy hearts among the brotherhood, this was done, and a tomb was built to forever keep him chained to the Binding Stone inscribed with magical runes that no mortal could decipher, should Tal Rasha himself falter. The Soulstone acted as a lock that prevented Baal from leaving the Binding Stone.
Seven identical tombs filled with perils were also made in the Canyon of the Magi, where the Tomb of Tal Rasha was made, to house the resting places of six other powerful Horadric mages. They also serve to confuse anyone looking to set Baal free. The canyon is located somewhere in the Aranoch desert, in the vicinity of Lut Gholein.
Eventually, Baal gained the upper hand but could not free himself from the Binding Stone as he was weak and required the Soulstone in his chest to be removed.
The Wanderer arrived with Marius to free him. Tyrael intervened and stopped the Wandered, but Marius was fooled by an illusion created by Baal, and freed the Prime Evil, which in turn helped the Wanderer chain Tyrael to the Binding Stone instead. A band of adventurers found and freed Tyrael in their hunt for the Wanderer.
What happened to the Tomb of Tal Rasha after Tyrael was freed is unknown.
Diablo II
In Diablo II, the only way to reach the Canyon of the Magi is from the Arcane Sanctuary, and the right tomb is marked with the one symbol missing from the sanctuary.
In the bottom of the true tomb, there's an orifice to enter the Horadric Staff, which leads to Tal Rasha's Chamber.
The other tombs are good for loot.