St Isaac's Cathedral

Saint Isaac's Cathedral or Isaakievskiy Sobor is a large architectural landmark cathedral that currently functions as a museum with occasional church services in Saint Petersburg, Russia. It is dedicated to Saint Isaac of Dalmatia, a patron saint of Peter the Great, who had been born on the feast day of that saint. It was originally built as a cathedral but was turned into a museum by the Soviet government in 1931 and has remained a museum ever since, with church services held in a side chapel since the 1990s. In 2017, the Governor of Saint Petersburg offered to transfer the cathedral back to the Russian Orthodox Church, but this was not accomplished due to the protests of St Petersburg citizens opposing the offer.

Source: Wikipedia