The St. Isaac` Cathedral is one of the largest cathedral in the world. The cathedral was originally the city's main church. It was built between 1818 and 1858.

The cathedral's facades are decorated with sculptures and massive granite columns (made of single pieces of red granite). The interior is adorned with incredibly detailed mosaic icons, paintings and columns made of malachite and lapis lazuli. Its inner decoration were made with mosaics instead of other artworks because of the difficulty of creating an ideal climate inside the vast building.

Some mosaic was made according to original artworks of T.A. Heff (1805-1875).