After more than 40 years archaeologists have finally reached the end of the mysterious tunnel in the tomb of Seti I. Yet hopes it would lead to the pharaoh's secret burial site have been crushed, after the seemingly unfinished tunnel suddenly stopped after a back-breaking 174m.

The tomb, in the Valley of the Kings, was first discovered in 1817 by strongman-turned-archaeologist Giovanni Belzoni. But despite being one of the site's most spectacular tombs, its strange tunnel wasn't excavated until the 1960s.

Back then a team led by Sheikh Ali Abdel-Rasoul took a wrong turn and workers abandoned the project around 130m in, fearing further digging could bring the tomb crashing down. Yet a excavation beginning in 2007, and led by Egyptian antiquities chief Dr Zahi Hawass, discovered a descending passage, 25.6m long and 2.6m wide, 136m into the partially-excavated tunnel. The team unearthed a myriad 18th Dynasty (1569 – 1315 BC) artefacts including shabtis, pottery fragments, limestone cartouches of Seti I and a model boat made from faience.

Using a mining car system and metal struts for support the passage was cleared, revealing a 54-step staircase, three of which had been covered in ancient red graffiti.

Remarkably a second staircase was then discovered, measuring 6m in length. At its entrance was a false door inscribed with hieratic instructions for the tunnel's builders: “Move the door jamb up and make the passage wider.” Yet hopes the tunnel would lead to the king's secret burial were dashed when it ended suddenly; its last step seemingly unfinished.

Dr Hawass says he was surprised to find a second staircase at all. Despite the tomb's ornate wall paintings, it also contains a large number of preliminary sketches of paintings which were never added, furthering the case that work on the tunnel was abandoned suddenly. Dr Hawass has speculated the tunnel was a symbolic path to the hidden tomb of Sokar, a god of the underworld. Yet he claims a connection with Seti's son Ramesses II is also likely.