This is possibly the biggest Communist-era monstrosity in Bulgaria, outshining even the Flying Saucer congress hall-cum-temple at Buzludzha.
It was erected in 1981 as part of a megalomaniacal project masterminded by Todor Zhivkov's daughter to mark the 1,300th anniversary of the foundation of the Bulgaria state, an euphemism for pumping up nationalism.
Now at least 30,000 tons of concrete stand exposed to the elements above a large Bulgarian city, but unlike Buzludzha this monument has not been abandoned. The local city council even charges entry fees to let you go into it. A particular favourite to Japanese and Israeli tourists (but for completely different reasons).
Where in Bulgaria are you?