Tal Rasha's Tomb is any one of seven secret tombs accessible from the Canyon of the Magi. Though there is only one True Tomb, the six false Tombs are also named Tomb of Tal Rasha in-game.
The True Tomb is marked near its entrance with a symbol noted from the end of the Arcane Sanctuary. At its end is an Orifice to place the Horadric Staff which opens a path to Tal Rasha's Chamber. The Orifice is guarded by a group of Horadric Mages led by Zoltun Kulle, whose death on Hell difficulty creates a portal to the Canyon of the Magi in the past.
The false Tombs usually have golden chests and one of them is home to the super unique Phantasm Warpwing.