This document lists several record-breaking mega structures that have been built in Turkey, including:
1) The Marmaray Tunnel in Istanbul, which is the deepest immersed tube rail tunnel in the world at 60 meters below sea level.
2) The Avrasya Tunnel in Istanbul, which is the world's deepest underwater road tunnel at 106 meters below sea level.
3) The 1915 Canakkale Bridge, which will be the longest suspension bridge in the world at 2023 meters long when completed in 2023.