The military hospital in the Bulgarian town Varna according to an American CIA report dated 7 April 1954

An item reported that in Grozdov Street, southeast outskirts of the Bulgarian town Varna a military hospital was situated near the Marine Park consisting of 3 large 4 story building to which a number of smaller1-storey building , some of which had a basement, was added.

Source
The report was published on www.archive.org, document number CIA-RPD80-00810A000500340010-8.