Palace Embankment, 30, Saint Petersburg, Russia, 191186
The Winter Palace's Spare House is a mansion (as well as a palace) built at the end of the 19th century by architect Nikolai Becker on the site of older 18th-century buildings. It is located in Saint Petersburg at the addresses Palace Embankment, 30 and Millionnaya Street, 31. The wing of the spare house is located on Millionnaya Street.
In the 1710s, the house on the plot now occupied by the Winter Palace's spare house was two stories high, had a high porch, and a sloping roof. This house belonged to Feodosy Sklyaev, a companion of Peter I, bombardier of the Preobrazhensky Regiment, and shipbuilder. Sklyaev had no heirs, so after his death in 1728, the house was transferred to the treasury. Notably, Sklyaev's house was located to the right of Peter's Winter Palace.

In the 1730s, Anna Ioannovna gifted the house and plot to Gustav Biron, brother of the Russian regent Ernst Biron. In the 1740s, the house was rebuilt, presumably by architect Carlo Giuseppe Trezzini, for Juliana Mengden, a lady-in-waiting and close friend of the ruler Anna Leopoldovna. At the beginning of the 19th century, the house passed to Countess Vorontsova, who initiated another reconstruction of the house and the construction of stone wings in the courtyard. One of these wings was rented out by the countess to the palace company of the Preobrazhensky Regiment. The Vorontsovs owned the house with its wings for about half a century until, in 1860, the palace department purchased the entire complex. The mansion became the Winter Palace's spare house.
In 1877–1878, under the direction of architect Becker, the main building (along the embankment) was rebuilt for Grand Duke Alexei Alexandrovich and took on its modern appearance; the wing on Millionnaya Street became four stories high. In 1885, Alexei Alexandrovich acquired a palace on the Moika River, and the house on Palace Embankment passed into the hands of Count Georgy Fyodorovich Mengden. The rebuilding of the building into a revenue house (finishing of residential and ceremonial rooms, as well as reconstruction of the wing) was carried out by academician Tikhobrazov. In the 1890s, Mengden's revenue house became the property of the court again, restoring its status as the Winter Palace's spare house.
In the early years after the October Revolution, the building housed the Petrograd Department of the Main Directorate for Museums and the Protection of Art, Antiquities, Folk Life, and Nature Monuments. In the 1930s, the house was occupied by employees of the Academy of Sciences, the Hermitage, and university professors.
Currently, the house is under the jurisdiction of the State Hermitage Museum. As early as 1988, it was directly connected to the other Hermitage buildings through the Hermitage Theatre, in the courtyard of which architect V. P. Lukin created a new gallery-transition on an arch.
In 2017, the Hermitage's scientific complex with the latest equipment was established here. The laboratory of scientific restoration of Eastern painting, located in the Spare House, is unique not only in Russia but worldwide.
Sources:
https://ru.wikipedia.org/wiki/Запасной_дом_Зимнего_дворца
Kolokolnaya St., 11, Saint Petersburg, Russia, 191025
pl. Ostrovskogo, 5, Saint Petersburg, Russia, 191023
Griboedov Canal Embankment, 2B, Saint Petersburg, Russia, 191186
Nevsky Ave., 28, Saint Petersburg, Russia, 191186
Zakharyevskaya St., 23, Saint Petersburg, Russia, 191123
Moika River Embankment, 73, Saint Petersburg, Russia, 190000
Kronverksky Ave, 7, Saint Petersburg, Russia, 197046
Nevsky Ave., 56, Saint Petersburg, Russia, 191023
Nevsky Ave., 56, Saint Petersburg, Russia, 191023
Gagarinskaya St., 3, Saint Petersburg, Russia, 191187
Nevsky Ave., 39, Saint Petersburg, Russia, 191023
Kazan Square, 2, Saint Petersburg, Russia, 191186
Nevsky Ave., 32-34, Saint Petersburg, Russia, 191186
Nevsky Ave., 17, Saint Petersburg, Russia, 191186
Kozhevennaya Line, 27, Saint Petersburg, Russia, 199106
Universitetskaya Embankment, 15, Saint Petersburg, Russia, 199034
Bolshoy Prospekt P.S., 75, Saint Petersburg, Russia, 197101
Rubinstein St., 7, Saint Petersburg, Russia, 191025
Malaya Morskaya St., 1, Saint Petersburg, Russia, 191186
Lensoveta St, 12, Saint Petersburg, Russia, 196135
TD "Burda Moden, Akademika Krylova St., 4, Saint Petersburg, Russia, 197183
38G5+75 Klypinykh Park, Saint Petersburg, Russia, 194362
15 Vologdina St., Saint Petersburg, Russia, 194362
New Peterhof, Bratyev Gorkushenko St., 9, Saint Petersburg, Russia, 198510
Avrova St., Building 2, Block 7, Saint Petersburg, Russia, 198510
VWJJ+8F Petrodvortsovy District, Saint Petersburg, Russia
Fontanka River Embankment, 54, Saint Petersburg, Russia, 191002
Saint Petersburg Ave., 15, Saint Petersburg, Russia, 198510
Kamennoostrovsky Ave., 1-3, Saint Petersburg, Russia, 197046
Bolshaya Alley, 14, Saint Petersburg, Russia, 197376
28 Tchaikovsky Street, Saint Petersburg, Russia, 191123
Kirochnaya St., 24, Saint Petersburg, Russia, 191123
Starorusskaya St., 5, Saint Petersburg, Russia, 191144
Kronverksky Ave, 1, Saint Petersburg, Russia, 197046
Kamennoostrovsky Ave., 24, Saint Petersburg, Russia, 197101
Kamennoostrovsky Ave., 26-28, Saint Petersburg, Russia, 197101
Sadovaya St., 21a, Saint Petersburg, Russia, 191023
Zagorodny Prospekt, 11, Saint Petersburg, Russia, 191002
7th Krasnoarmeyskaya St., 32, Saint Petersburg, Russia, 190005
Arsenalnaya Embankment, 7, Saint Petersburg, Russia, 195009
1st Elagin Bridge, 1, Saint Petersburg, Russia, 197183
Saint Petersburg, Kirochnaya 8 lit V, Saint Petersburg, Russia, 191028
Palace Embankment, 26, Saint Petersburg, Russia, 191186
Bolshaya Morskaya St., 3-5, 6th floor, office 3, Saint Petersburg, Russia, 191186
Bolshaya Morskaya St., 58, Saint Petersburg, Russia, 190000
Nevsky Ave., 36, Saint Petersburg, Russia, 191186
Fontanka River Embankment, 92, Saint Petersburg, Russia, 191180
Millionnaya St., 5/1, Saint Petersburg, Russia, 191186
Sadovaya St., 55-57, Saint Petersburg, Russia, 190068
Isaakievskaya Square, 1, Saint Petersburg, Russia, 190000
Kamennoostrovsky Ave, 5, Saint Petersburg, Russia, 197046
10 Mira St., Building A, Office 25, Saint Petersburg, Russia, 197101
Kamennoostrovsky Ave., 44B, Saint Petersburg, Russia, 197101
Bolshoy Prospekt P.S., 44, Saint Petersburg, Russia, 197198
4th Line V.O., 13, Saint Petersburg, Russia, 199034
Vladimirsky Ave., 19, Saint Petersburg, Russia, 191002
Vvedenskaya St., 7, Saint Petersburg, Russia, 197198
Gatchinskaya St., 11, Saint Petersburg, Russia, 197136
Universitetskaya Embankment, 11, Saint Petersburg, Russia, 199034
Budapest Street, 103/49, Saint Petersburg, Russia, 192283
Piskaryovsky Ave, 3, Saint Petersburg, Russia, 195027
Bolshaya Porokhovskaya St., 18, Saint Petersburg, Russia, 195176
Malaya Morskaya St., 24, Saint Petersburg, Russia, 190000
Fanerny Lane, 11, Saint Petersburg, Russia, 196643
Kuznechny Lane, 6, Saint Petersburg, Russia, 197720
Gorokhovaya St., 4, Saint Petersburg, Russia, 191186
32 Tchaikovsky Street, Saint Petersburg, Russia, 191123
Nevsky Ave., 65, Saint Petersburg, Russia, 191025
Obukhovskoy Oborony Avenue, 235, Saint Petersburg, Russia, 192012
Nevsky Ave., 12, Saint Petersburg, Russia, 191186
Staro-Petergofsky Ave., 19, Saint Petersburg, Russia, 190020
Shpalernaya St., 37, lit. A, Saint Petersburg, Russia, 191123
Petrovskaya Embankment, 6, Saint Petersburg, Russia, 197046
Building A, Saint Petersburg, Russia, 191186
Mars Field, 9, Saint Petersburg, Russia, 191186
Sadovaya St., 62, Building A, Saint Petersburg, Russia, 190068
Moika River Embankment, 3, Saint Petersburg, Russia, 191186
Apraksin Dvor, Saint Petersburg, Russia, 191023
Malaya Sadovaya St., 2, Saint Petersburg, Russia, 191023
Mokhovaya St., 48, Saint Petersburg, Russia, 191028
English Embankment, 56, Saint Petersburg, Russia, 190121
Alexandrovsky Park, 4, Saint Petersburg, Russia, 197198
Maly pr. P.S., 69, Saint Petersburg, Russia, 197136
Millionnaya St., 9, Saint Petersburg, Russia, 191186
Fontanka River Embankment, 25, Saint Petersburg, Russia, 191023
Isaakievskaya Square, 6, Saint Petersburg, Russia, 190107
4 Kvarengi Lane, Saint Petersburg, Russia, 191060
12 Kryukov Canal Embankment, Saint Petersburg, Russia, 190068
Bolshaya Pushkarskaya St., 9, Saint Petersburg, Russia, 197198
English Embankment, 4, Saint Petersburg, Russia, 190000
Kirochnaya St., 14, Saint Petersburg, Russia, 198411
Fontanka River Embankment, 3, lit. A, Saint Petersburg, Russia, 191028