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 Romanov ladies from an English point of view. George Dawe, artist. Living from 1781 to 1829 he spent the last ten years of his life painting in Saint Petersburg.

Tsarina Alexandra Feodorovna, wife of Tsar Nicholas I. 1820's.
Tsarina Alexandra Feodorovna, wife of Tsar Nicholas I. 1820’s. Workshop of George Dawe. In the public domain because the artist died over 70 years ago. via https://commons.wikimedia.org/wiki/File:Alexandra_Feodorovna_-_workshop_of_G.Dawe_(1820s,_GIM).jpg
Tsaritsa Marie Feodorovna, widow of Paul I. 1825.
Tsaritsa Marie Feodorovna, widow of Paul I. 1825. Collection of the Hermitage Museum, Saint Petersburg. In the public domain in the United States because the artist has been dead over 70 years. via http://www.gogmsite.net/russian1715-1789/subalbum-tsaritsa-maria-feo/widow-maria-feodorovna-by.html
Grand Duchess Maria Pavlovna of Russia. 1822.
Grand Duchess Maria Pavlovna of Russia. 1822. Collection of the Hermitage 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:Maria_Pavlovna_of_Russia_by_G.Dawe_(1822,_Hermitage).jpg

Winter gardens from an earlier time . Rich enough to stay inside and never come out, making it no wonder that two of these show the tsar’s own palm trees and two more those of the Yusopovs, who made the tsar and his diamonds as big as eggs look a little on the minimal side.

"Winter Garden of Empress Alexandra Fyodorovna." 1860's.
“Winter Garden of Empress Alexandra Fyodorovna.” 1860’s. Konstantin Andreyevich Ukhtomsky,(1818-1881). Collection of the Hermitage Museum, Saint Petersburg. via https://www.arthermitage.org/Konstantin-Andreyevich-Ukhtomsky/Interiors-of-the-Winter-Palace-The-Winter-Garden-of-Empress-Alexandra-Fyodorovna.html.
"The Winter Garden" from the series "Interiors of the Small Hermitage." 1865.
“The Winter Garden” from the series “Interiors of the Small Hermitage.” 1865. Edward Hau, watercolorist (1807-1888). Collection of the Hermitage Museum. via https://commons.wikimedia.org/wiki/File:Hau._Interiors_of_the_Small_Hermitage._The_Winter_Garden._1865.jpg.
"The Interior of the Palm House on the Pfaueninsel near Potsdam." 1834.
“The Interior of the Palm House on the Pfaueninsel near Potsdam.” 1834. Carl Blechen (1798-1840). Collection of the Art Institute of Chicago. Cc Licence via 1.0. via https://commons.wikimedia.org/wiki/File:The_Interior_of_the_Palm_House_on_the_Pfaueninsel_near_Potsdam,_1834,_by_Carl_Blechen_-_Art_Institute_of_Chicago_-_DSC09556.JPG
Winter Garden, Yusupov Palace, Saint Petersburg. 1852.
Winter Garden, Yusupov Palace, Saint Petersburg. 1852. V.S.Sadovnikov, artist. via https://terijoki.spb.ru/old_dachi/od_articles.php?item=12.
Winter Garden of the Yusupov Palace, Saint Petersburg. 1862.
Winter Garden of the Yusupov Palace, Saint Petersburg. 1862. A.A.Redkovsky, artist. via https://www.liveinternet.ru/users/4000579/post371616532.

All Russian art in the public domain because the artists have been dead over 100 years.