There's a small Mexican restaurant I used to go to in Thibodaux, LA and the owners are from there. There's a picture of the city on the wall by the cash register and even though I haven't been in years, that photo looks very familiar to theirs.
You're very close and I would say correct! Actually it is the Russian Zoological Institute in front of the old Stock Exchange building (just the roof is visible) on Vasilievsky Island in the Neva River.
I could pick out Poseidon on the blgd with the trident (and maybe another one of him near the water). I googled Poseidon and Neptune on building. Popped right up. Pretty neat looking place.
This one should keep you guys busy for a few minutes. Even though my son took this pic, it's a "photospot", so don't google-image it or it will pop right up.
[edit: that doofus in the picture is NOT my son, it's his friend; no subirse en el muro derp]