I think it would be the Central Siberian Plateau.
If you don't know it is Lake Baikal
north hemisphere
Lake Baikal is in eastern Russia, just north of Mongolia
Lake Baikal is also known as the North Sea and is the largest fresh water lake in the world. It is located in the south of the Russian region of Siberia.
The Angara River leaves Lake Baikal at Port Baikal/Listvyanka from where it flows north and west until it runs into the Yenisey River north of Krasnoyarsk and flows into the Kara Sea.
Lake Baikal.
Lake Baikal
Lake Baikal, Russia is in the Northern Hemisphere as it is North of the Equator. Also, it is in the Eastern Hemisphere as it is to the East of the Prime Meridian.
Lake Baikal
Lake Baikal in Russia contains more water than the North American Great Lakes combined.
Lake Baikal is located at approximately 105.0° East longitude. It is situated in Siberia, Russia, and is the deepest and oldest freshwater lake in the world. The lake's coordinates also include a latitude of about 53.5° North.