Well we thought we had seen all the sights of St Petersburg but the Captain told us about the St Petersburg Dam that was constructed to protect the port. The complex is intended to protect Saint Petersburg from storm surges by separating the Neva Bay from rest of the Gulf of Finland.
Construction began in 1978. It was completed by Putin in 2011. The dam spans the Gulf of Finland with the island of Kotlin (Kronstadt) at its centre. It extends for 25.4 km and stands 8 m above sea level. It incorporates two large openings for shipping, which can be closed when floods threaten.
As there were so many cruise ships leaving we were delayed until 7 pm as it is single file through the shipping channel at Kotlin. So we chose to stay on deck to watch and it was a fascinating few hours.
When we got closer to the opening in the wall, we could see cars driving from both sides and then we realised there was a tunnel (1.2 metres long) under the opening to the Gulf of Finland.
It was evident that the Island of Kotlin had been used as a fortress to protect the city in previous ages as we saw remnants of cannons etc. There are 3 main bays around Kotlin, one of which is used for the Russian naval vessels when required.