Countess Karlova's mansion, Baroque Revival mansion on the Fontanka, Saint Petersburg, Russia

Countess Karlova's mansion is a Baroque Revival structure along the Fontanka River in Saint Petersburg, decorated with ornate architectural elements and intricate details across its facade. The property sits at number 46 on the embankment and overlooks the river with the characteristic features of late 18th century design.

The estate is first documented in 1736, when Ulian Sinyavin's plot was bought by Antoine Cormedon; by 1740 it belonged to General Biron. After Biron's exile it passed to Fedor Dubyansky, who built a wooden house on a stone base in Russian Baroque style. In 1843 architect V. Ya. Langwagen added a third storey to the wings for General N. V. Zinoviev, and in 1895 Duke G. G. Mecklenburg-Strelitz acquired it, followed by his widow Countess N. F. Karlova.

The mansion houses the Prince Golitsyn Memorial Library, opened in 1994 by the London-based charity Golitsyn to St Petersburg in memory of Prince Georgy Golitsyn (1916–1992). Its core is books on Russia published abroad in Russian and English, many unavailable to Soviet readers, often bearing donors' inscriptions. The library's bookplate combines the arms of the Mecklenburg-Strelitz dukes and the Golitsyn princes.

The site opens to visitors during set hours so you can explore its architecture and library collections. It helps to check ahead since it functions as a working library with possible restrictions in certain areas.

The pediment carries the motto Fuimus et sumus ("we were, and we are"), placed there by Duke Georg of Mecklenburg-Strelitz, who bought the estate in 1895. In the garden stands a fountain added between 1934 and 1956, most likely in the second half of the 1950s.