The vast golden dome dominating the St Petersburg skyline is the neo-classical St Isaac's Cathedral. French designer Ricard de Montferrand kick-started proceedings in 1818, but construction took so long (the cathedral wasn't finished until 1858) that Nicholas I was able to extend the original designs to include even more extravagance.

The granite was ordered from Finland (and delivered in specially built ships and railways), 100kg (220lbs) of gold leaf were used for the dome and the end result - a lavish interior of marble and mosaic - is a must-see. You can climb up the 43m-high (141ft) colonnade for breathtaking views of the city.