Trångsund Fortress — 19th-century defensive structures, the remains of which have been preserved on the outskirts of the town of Vysotsk. It was created on the islands of the Vyborg Bay to protect the water approaches to Vyborg.

The first fortifications on Vysotsky Island were built during the Great Northern War to protect Vyborg, besieged by Russian troops, from the sea. The name "Trångsund" (narrow strait) comes from the Swedish name of the strait between Vysotsky and Maly Vysotsky Islands, the width of which at its narrowest point is about 180 meters — this is the main of the three fairways leading to Vyborg. In 1710, when the town of Trångsund (now Vysotsk) was founded, batteries already existed — they fought successful battles against the Swedish fleet. No traces of buildings from the Peter the Great era have yet been discovered.

The construction of the fortress that has survived to this day began one and a half centuries later, in 1864, and was completed in 1867. Trångsund Fortress was a rather powerful complex of batteries, bastions, and casemates carved into the granite rocks of the island’s shore along the strait. However, due to the rapid development of firearms and artillery during this period, by the 1880s it was considered morally outdated and of little effectiveness. Initially, to control the Trångsund Strait, "8-inch Krupp guns were installed, namely two in the Trångsund redoubt and four in the Pechorskaya battery."

By the beginning of the 20th century, the fortress was disarmed and did not participate in the Crimean War, when the allied Turkish fleet approached Kronstadt closely, nor was it involved in World War I or the Civil War. Even when the thrifty Finns came here, they did not include it in the famous Mannerheim Line. After 1917, the town of Trångsund along with the fortress, like the entire former Vyborg Governorate, became part of independent Finland and was renamed Uuras. Since then, Trångsund Fortress has not been used (except for episodes of the Winter War, when fighting took place on the territory of the already abandoned fortifications) and has gradually fallen into ruin.

Even when the thrifty Finns came here, they did not include it in the famous Mannerheim Line. In 1941, the island was occupied by Finnish and Nazi German troops, and in 1944 it was retaken. Four years later, the archipelago and the island were named after the Hero of the Soviet Union, machine gunner Kuzma Vysotsky. He died at this place in 1940. In the 1960s, Finland leased the small island Maly Vysotsky and the channel that Trångsund Fortress was supposed to protect. This lease was extended until 2063, so ships flying the Finnish flag are most often seen in the waters.

Currently, the fortress territory is overgrown with forest. Earth ditches faced with granite blocks, gates, curtains, and interior rooms have been preserved, most of them in a ruined state.

Since its disarmament, the fortress buildings have gradually become overgrown with forest and are slowly deteriorating. However, everything has been quite well preserved to this day. No guns with shells can be seen here, but you can study the granite ramparts and powerful brick casemates.

Sources:

https://ru.wikipedia.org/wiki/Trångsund_(fortress)