In Isopuisto on Kotkansaari stands the oldest building in Kotka. The Church of St. Nicholas was built between 1799 and 1801 and is the main church of the Orthodox congregation in Kotka.

The neoclassical Church of St. Nicholas dates back to the time of the fortress town of Ruotsinsalmi. A small part of the cemetery, along with its memorials, has been preserved next to the church. The cemetery is the final resting place of notable officers from the Ruotsinsalmi sea fortress.

For modern-day Kotkans, the Church of St. Nicholas offers a beautiful sight during picnic moments spent in Isopuisto.