The dome of Bulgaria’s biggest planetarium, built in 1975, is the mirror image of the equally broad, navy-coloured cathedral cupola opposite. Architectural harmony aside, the planetarium offers shows (35 to 40 minutes) that explain the story of the universe and the mysteries of time, space and UFOs. Check the website for show times; at the time of writing, 3pm was a guaranteed session while others depended on visitor numbers. Foreign-language sessions are at 2pm.