Designed after plans by architect Auguste de Montferrand, St Isaac's Cathedral and its spectacular dimensions were built between 1818 and 1858 by some 400 000 workers! Everything here is outsized. It is supported by 24 000 piles and contains 350 statues and reliefs on its façade, as well as 112 columns; its sumptuous interior decor required 400kg of gold, 1 000t of bronze, 16t of malachite and over 11m of lazurite. Admire the frescoes and murals, such as the one by Karl Briullov covering 800 m2 of the main dome.