F-4 Object

The F-4 Object (publicly often known as the Rákosi-bunker, Hungarian: F-4 objektum/Rákosi-bunker) is a formerly secret nuclear shelter under the downtown of Budapest. It is located 45-50 metres below the surface, several kilometres long approximately in a "H" shape between Kossuth tér and Szabadság tér.

It has a direct connection to the Line 2 of the Budapest Metro and a closed tunnel to the Hungarian Parliament Building. According to other sources, the bunker has a connection with the former headquarters of the Hungarian Working People's Party (located over the structure), and there is no tunnel to the Parliament Building.