This structure would have been built on the order of Sety I in homage to  Osiris. The name of Osireion was given to him by Petrie. The central part is a platform of granite surrounded with a channel that had to make appear it like an island. The level of water being now over several meters to the of the one of the time of Sety, the Osireion is flooded and it is impossible to visit it.  It is a curious monument, made of massive enough blocks that are precisely in the alignment of the temple. Its sense remains mysterious:. The decor has been performed under Merenptah (Vandersleyen, 1995).  On its walls are drawn illustrations of the Book of Gates, the Books of Caverns and the Book of Nut.  The work of Murray (1904) gives account of the first discoveries and makes a complete enough description of the rooms, except the Sarcophagus room.

The Osireion is constructed like a tomb with a sarcophagus chamber. You can see the map from Porter and Moss (Vol. VII, 2002), amended so that orientation is the same that the one of the map of the Sety  temple. The Osireion was overlayed of sand, and has been cleared in the beginning of the 20th century. The room of the sarcophagus has been discovered by Naville in 1915. Above on the photo one can see the central hall and its pillars. The photo has the same orientation than the map.