Saint Michael's Castle — also called the Mikhailovsky Castle or Engineers' Castle — is the deep terracotta-coloured fortified palace built for Tsar Paul I in 1797–1801. It is unmistakable: a four-square pile with a moat, a chapel topped by a spire, and a distinctive red-orange colour that legend says was chosen to match the gloves of Paul's mistress. Inside, the rooms now belong to the Russian Museum and house a rotating display of 18th- and 19th-century Russian portrait painting.
The castle is just across the Moika from the Field of Mars and only a few minutes' walk from the Church of the Savior on Spilled Blood, so it slots easily into a day around the upper Nevsky. The Bronze equestrian statue of Peter the Great on the south side — by Bartolomeo Carlo Rastrelli, father of the architect — is older than the more famous Bronze Horseman on Senate Square but far less seen.