The F4 Object or Rákosi bunker is a formerly secret nuclear shelter under the downtown of Budapest. It is located 39 meters below the surface, 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 presumably to the Hungarian Parliament Building.
Its construction began in 1949 parallel with the metro. Its goal was to provide shelter to Mátyás Rákosi and the Central Committee members of the Hungarian Working Peoples Party in case of a possible nuclear raid, as well as to provide space for offices of the Parliament. When the danger is over, they were supposed to take the metro to Eastern railway station and then change to an armored train. It was made technologically similarly to a metro (it resembles metro stations and tunnels), so the workers were informed they were building the metro. According to rumours, hundreds of prisoners worked at the construction, while in fact this work was done by miners.
The object, suitable to accommodate 2200 people, with an area of 3500-3800 square meters, was completed in 1953.  An emergency exit was created next to the Hungarian Television headquarters, also serving for ventilation. The object, resembling a labyrinth, houses a separate council hall, intended for the leaders of the country to debate the current tasks. Though never used, it was kept at the ready until the mid-1970s. The shelter was revealed to the public in the 1994 documentary film titled Pincebörtön [A Cellar Prison].
The present time you can not entrance the object, it is closed for the public, but if you would like to visit the emergency exit, you can find it on the Szabadság tér/square.
Address: Szabadság square, Budapest 5.