Hagia Sophia attracts thousands of visitors and is one of the main attractions of Istanbul. However, this mosque has many tunnels, cellars and graves that are being uncovered underneath as you read this! 
Two years ago some researchers were able to 3D map the tunnels under the hagia sophia some of which are about 1 kilometer long.
4 meters beneath the surface, rests a three chamber tomb as well. This tomb is dated back to 4th century A.D! This tomb is the oldest structure that you can find next to Hagia sophia!
Most of the tunnels and underground passages under hagia sophia were built as ventilation and plumbing systems. therefore, most of them are very narrow to explore. The knowledge of these tunnels has led to some urban legends that hagia sophia extends as far as the Maiden's Tower and Princes' Islands.
As the explorations continue, who knows what historical pieces might be un earthed from hagia sophia.
Two years ago some researchers were able to 3D map the tunnels under the hagia sophia some of which are about 1 kilometer long.
4 meters beneath the surface, rests a three chamber tomb as well. This tomb is dated back to 4th century A.D! This tomb is the oldest structure that you can find next to Hagia sophia!
Most of the tunnels and underground passages under hagia sophia were built as ventilation and plumbing systems. therefore, most of them are very narrow to explore. The knowledge of these tunnels has led to some urban legends that hagia sophia extends as far as the Maiden's Tower and Princes' Islands.
As the explorations continue, who knows what historical pieces might be un earthed from hagia sophia.