Watercolors of Saint Petersburg by Russian watercolorist Vasily Sadovnikov. Living from 1800 to 1879, (1800-1879), he was a leading Russian master of perspective painting. Painted many interiors too.

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“Palace Square, Saint Petersburg.” 1830s. Russian. Watercolor and grottage on paper. Collections of the the Pushkin Fine Art Museum. In the public domain in the United States because the artist has been dead over 70 years. via https://commons.wikimedia.org/wiki/File:PalaceSquare-Sadovnikov.jpg
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“The Mariinsky Palace.” 19th c. In the public domain due to age. via https://www.flickr.com/photos/amber-tree/30284826772/
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“Court Departure at the Main Entrance of the Great Palace.” 1852. Image via wikigallery.org. Artwork in the public domain due to age. via http://www.wikigallery.org/wiki/painting_163340/Vasili-Semenovich-Sadovnikov/Court-Departure-at-the-Main-Entrance-of-the-Great-Palace%2C-1852
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“View of the Palace square and the Winter Palace in Saint Petersburg.” 19th c. Image © Arthive, 2020. Fair use license. via https://arthive.com/artists/1921~Vasily_Semenovich_Sadovnikov/works/28806~View_of_the_Palace_square_and_the_Winter_Palace_in_St_Petersburg
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“View of the Anichkov Palace from the Fontanka River.” 1838. Source: communitylivejournal.com. In the public domain because the artist has been dead over 70 years. via https://commons.wikimedia.org/wiki/File:Fontanka_anichkov_1838.jpg

Imperial Russia. Watercolors of something that seems only dreamt up but once was real. These by Russian watercolorist Vasily Sadovnikov (1800-1879), who was a leading Russian master of perspective painting.

Room in the house of the princes Golitsyn. 1845.
Room in the house of the princes Golitsyn. 1845. Private collection. In the public domain due to age. via https://arthive.com/artists/1921~Vasily_Semenovich_Sadovnikov/works/13728~The_interior_room_in_the_house_of_the_princes_Golitsynyh
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“Nicholas Hall” from the album “Interiors of the Winter Palace.” 1857. Collection of the Hermitage Museum, Saint Petersburg. In the public domain due to age. via https://www.arthermitage.org/Vasily-Semyonovich-Sadovnikov/Interiors-of-the-Winter-Palace-The-Nicholas-Hall.html
The Field Marshal's Hall of the Winter Palace. 1852.
The Field Marshal’s Hall of the Winter Palace. 1852. In the public domain due to age. via https://commons.wikimedia.org/wiki/File:Field_Marshal%27s_Hall,_Sadovnikov.jpg
"Arch of the General Staff building." 1830s.
“Arch of the General Staff building.” 1830s. Image courtesy staratel.com. In the public domain due to age. via https://commons.wikimedia.org/wiki/File:Sadovnikiov_Arch_of_General_Stuff_Building_1830s.jpg