The construction started in 1909 on the shore of Gulf of Finland, cape Inoniemi.
Construction continued until 1917, but main fortifications were ready in 1912 (start of World War I).
Fort Ino (on the northern shore of the gulf), Krasnaya Gorka (on the southern shore) and forts of Kronstadt (in between) created a single line of defence.
(the photos show mostly the 12-inch tower battery - the most powerful battery of the fort).
A curious fact - since at that time this was Finland's territory (then part of the Russian Empire), local Finnish workers were employed for the construction. However, the ministry of home affairs soon discontinued the practice, in order to keep the structure of the fortifications a secret.
It is not quite clear, how the Finns were different in this respect from, say, Ukrainians, who were also part of the Empire.
In 1918 the soviet government granted independence to Finland, and the fort Ino became part of foreign territory.
There was, however, an agreement which could see Finland cede the fort in exchange for other territories. However, after the Finnish Civil War was won by the Whites, the new government did not favour the exchange. There was an attempt to defend the fort. As this could lead to a conflict with the Germans (allies of the Finns) and a breach of the Treaty of Brest-Litovsk, Council of the People's Commissars of Russia ordered to destroy the fort if it could not be defended by the forces of the garrison. As a result, on 14 May 1918 the fort was blown up with 300 poods (4914 kg) of pyroxylin.
Thus, the fort has never happened to see battle.
The fort was quite thoroughly destroyed.
Some underground spaces remain, but the entrances are mostly blocked (they say, this was partly done later, to prevent children climbing in).
The remaining cannons, armour and materials were removed by the Finns and used, in particular, to build fortifications for the Winter War of 1939.
In 1920, the Finns, according to the Treaty of Tartu, blew up whatever survived the first explosion.
Originally, there were a lot of wooden buildings (barracks, quarters, etc.), but none of them survived to present day.
"Plateau" - a concrete roof, the spaces underneath were used for different purposes: the arsenal, etc.
Here was a 305mm cannon.
There are different sorts of holes in the ground - fall into them, and the flight will take a while.