The 1500m passage – which is around 1.8m high and contains two stone heads – was unearthed by a group of archaeologists who hailed it as a “geometric miracle”.
The discovery was a part of the Egyptian Dominican archaeological mission of the University of San Domingo, led by Dr. Kathleen Martinez.
Last week, the Egyptian Ministry of Tourism and Antiquities announced the successful mission, revealing that Martinez and her team uncovered the tunnel.
It was found below the ground “during archaeological excavations of the mission in the area of the Temple of Tapozeries Magna”, west of Alexandria.
For years, Martinez has believed that Egypt’s final pharaoh Cleopatra may have been laid to rest in the temple – alongside her lover Mark Antony.
Speaking to Heritage Key, Martinez said: “This is the perfect place for the tomb of Cleopatra.
“If there’s a one per cent chance that the last queen of Egypt could be buried there, it is my duty to search for her.
“If we discover the tomb … it will be the most important discovery of the 21st century.
“If we do not discover the tomb … we made major discoveries here, inside the temple and outside the temple.”
Cleopatra VII was born in 70 or 69BC and ruled Egypt as coregent for almost 30 years.
Following her death, Egypt was annexed by its Roman rulers, effectively ending the 3000-year-old Ancient Egyptian Empire.
Pharaohs often built huge tombs to be buried in, but given her status as a prisoner of Rome at the time of her death, it’s likely Cleopatra was given a quiet burial in an austere tomb.
Cleopatra, the last queen of Egypt, is one of history’s most famous female rulers, but her final resting place remains an unsolved mystery.
Some experts believe the beautiful seductress was buried in Alexandria, where she was born and ruled for most of her life.
Others suggest she was laid to rest at the ancient site of Taposiris Magna.
Sitting 30 miles from Alexandria, the temple’s surrounding city of the same name was a prominent port town during Cleopatra’s time.
Citing preliminary studies, the Ministry claimed the tunnel is eerily similar to the Eubilinos Tunnel in Greece – which served as an aqueduct – however the Egyptian one is longer.
Within the tunnel, the archaeologists found two heads.
“One of them belongs to a person from the heroic age, and the other is probably a statue of Father of the Spook,” the Ministry said.
Martinez told LiveScience.com that they also found coins and the remains of statues of Egyptian deities in the tunnel.
In their excavations and surveys, the archaeologists found that part of the tunnel was “submerged under the Mediterranean,” according to the Ministry.
They found pottery and a “rectangular block of limestone” under the mud sediment.
The Egyptian Ministry of Tourism and Antiquities confirmed that the discovery of part of the tunnel being underwater, confirmed the archaeologists’ suspicions that part of the temple’s foundation is also submerged.
The archaeologists’ work on the temple has proven difficult, as at least 23 earthquakes hit the region between 320AD and 1303AD – which caused part of the temple to collapse.
Previously, however, the team has uncovered important artefacts inside the temple, including coins that featured the names and images of Cleopatra VII and Alexander the Great.
They have also found several beheaded statues and the statues of the goddess Isis, the ministry said.
Additionally, the archaeologists have discovered a network of tunnels from King Mariout Lake in Alexandria to the Mediterranean.