© Bin im Garten - CC BY-SA 3.0

The National Palace of Culture (Национален дворец на културата, Natsionalen dvorets na kulturata; abbreviated as НДК, NDK), located in Sofia, the capital of Bulgaria, is the largest, multifunctional conference and exhibition centre in south-eastern Europe. It was opened in 1981 in celebration of Bulgaria's 1300th anniversary. (Wikipedia)

Wikipedia National_Palace_of_Culture#Concerts
Capacity 3876
Address National Culture Palace, Bulevard "Bulgaria", 1463 Ndk , Sofia, Bulgaria
Architect Alexander Georgiev Barov, Atanas Agura and Ivan Kanazirev
Opening year 1981, March 31st
Official website http://www.ndk.bg/