The Saint Petersburg Metro is located deep underground.
With around 2.15 million passengers per day using the network.
For this reason ventilation shafts are an important feature – they allow fresh air to reach the tunnels far below ground level.
The first ventilation shaft I found was near Gorkovskaya station on line 2, in the grounds of Alexander Park.
They also appear in the middle of the city, such as this shaft outside Ploshchad Vosstaniya (Плóщадь Восстáния) station on line 1.
The third one I found was in the Field of Mars (Ма́рсово по́ле), a short distance from Saint Michael’s Castle.
I wonder how many other ventilation shafts exist across the network?