The weighty mass of St.Isaac's Cathedral dominates the skyline of St.Petersburg. Its gilded dome, covered with 100 kg of pure gold, soars over 100 meters into the air, making it visible far out onto the Gulf of Finland. It is now the third biggest Cathedral in the world.

St.Isaac was the patron saint of the Romanov family. The present version of St.Isaac's, the fourth, was constructed from 1818 to 1858. The original St.Isaac's, a small wooden church, was located near the Admiralty. Peter I and Catherine I were married here in 1712. Soon afterwards it was agreed that the decrepit structure did not suit the emerging grandeur of the capital and in 1717 a stone of St.Isaac's was built on the spot now occupied by the Bronze Horseman. Then in the 1760s Catherine II decided she wanted a huge marble St.Isaac's, and construction began on the third version in 1768. This dragged on until it was hastily completed in 1802, but the result was different from the original plan and was neither pretty nor well built. When rotten ceiling plaster fell from high on an Easter service in 1816, Alexander I decided to get the St.Isaac's business finished once and for all.

By the time the cathedral was completed in 1858, its cost had spiraled to more than twenty million rubles — as well as the lives of hundreds of laborers.

Mosaic paintings and icons, ornate marble slabs, as well as columns decorated with malachite and lapis-lazuli dazzle the eye inside the cathedral. St.Isaac's was closed in early 1930s and later turned into a museum. Nowadays, church services are held on major occasions only.