The Memorial Museum of Astronautics opened in Moscow in 1981. Why underground? Because it is located within the base of the soaring Monument to the Conquerors of Space in the northeast of the city.
Though the space monument's tower was erected in 1964, the memorial museum did not exist for another seventeen years. Opening ceremonies took place on April 10, 1981, to commemorate the 20th anniversary of the day Yuri Gagarin became the first human to orbit the Earth in space.
Busts of astronauts: Gagarin, Tereshkova, Komarov, etc.
A monument to Tsiolkovsky and Monument to the Conquerors of Space.