Directly behind the Temple of Seti I, the Osireion is a weird and wonderful structure, unique in Egypt and still baffling for Egyptologists. The entire structure is closed to visitors, making inspection of the funerary and ritual texts carved on its walls impossible, but you can look down on it from the rear of Seti's temple, from where there is a good overview of the cenotaph and its surrounding waters.
Originally thought to be an Old Kingdom construction, on account of the great blocks of granite, it has now been dated to Seti’s reign and is usually interpreted as a cenotaph to Osiris, or more specifically to Seti as Osiris. Its design is believed to be based on the rock-cut tombs in the Valley of the Kings. Reached by a 420-ft subterranean passage, the centre of its 10-columned ‘burial chamber’, which lies at a lower level than Seti’s temple, is a dummy sarcophagus. This chamber is surrounded by water channels to simulate an island.