The St.Isaac’s cathedral is a former principal cathedral of the Russian Empire. This is the fourth largest cathedral in the world after St.Peter’s in Rome, St.Paul’s in London and St.Maria in Florence. The cathedral was consecrated in 1858. It had been under construction for more than forty years. According to the legend the architect Montferrand after whose project the cathedral was built was predicted that he would die immediately after the completion of the cathedral: probably this was the reason for such a delay in construction. And true, the architect died soon after the consecration.
Be sure to get up to the collonade: from this viewing platform, you can admire the city’s panorama from the bird’s flight.
Today the cathedral is mainly used as a museum. But it is also place of worship: in the smaller altar services are still being held.
For more http://eng.cathedral.ru/isaac