The Saint Petersburg Flood Prevention Facility Complex is the 25-kilometre dam and barrier system that connects Kotlin Island to the mainland on both sides, carrying the ring road that links Kronstadt to St Petersburg and the shore communities. The dam was one of the largest infrastructure projects in Soviet and post-Soviet Russia: begun in 1980, suspended for lack of funds in the 1990s, and finally completed in 2011.
The barrier protects St Petersburg from the catastrophic floods that devastated the city throughout its history — the worst, in 1824, submerged much of the city under four metres of water. Crossing the dam to reach Kronstadt gives an unusual perspective: you drive across the open Gulf of Finland with views in all directions, through the central navigation gate, and out onto the island. The structure itself is engineering on a vast scale and worth appreciating even if you have no particular interest in flood control.