Catherine the Great ordered construction of a new defence line to protect St. Petersburg. The result was a series of three fortification chains, the southernmost part of the outer chain being the Ruotsinsalmi sea fortress. Later the city of Kotka was founded on the ruins of the Ruotsinsalmi fortress. In the first phase of construction 1790-1796 the major forts were built. Catherine's Trail shows the history of the fortress garrison period of Fort Catherine. The path starts from the Sapokka water park area. The path takes visitors through the period of the fortress community at Empress Catherine the Great's Ruotsinsalmi.

The herb garden set up in the Kotka Redoubt, a small renovated fortress construction at Ruotsinsalmi, exudes an atmosphere of bygone times. The herb garden is on Haukkavuorentie and has about a hundred herb and spice plants. The garden's designers took special account of the needs of the visually impaired. For example, the herbs have Braille labels. The herbs also attract butterflies and other insects. The varied shapes, the attractive colours and rich aromas of the herbs offer pleasures for all the senses.

The fortification island of Varissaari-Fort Elisabeth just off Kotka and the services there make an island day trip destination. There is an unobstructed view of the site of the Ruotsinsalmi sea battles (1789-1790) from the ruins of the ramparts of Fort Elisabeth and the museum restaurant. Also on the island, articles from the frigate St. Nikolai which sank off the coast of Kotka and the monument to the II sea battle (9.7.1790) unveiled in 1940 bear witness to the battles. Varissaari is about 10 minutes by motor launch from the jetty at Sapokanlahti Bay.

Kukouri - Fort Slava is a round stone fortification faced with red brick. It was completed off Kotka in 1794 as part of the Ruotsinsalmi - Kyminlinna fortification chain. Fort Slava was used as a prison in the 1820s and 1840s. The rest of the Ruotsinsalmi sea fortress had already been disbanded in the 1830s, but a small guard detachment remained at Fort Slava.. During the Crimean War in summer 1855 the Anglo-French fleet destroyed the abandoned fortress. Nowadays Fort Slava has been partially repaired and parts are open to tourists.