Linnahall Kalamaja & Telliskivi

Resembling a cross between a nuclear bunker, a WWII sea-fort and some inscrutable temple to a vanished god, the Linnahall is in fact a covered concrete arena built for the 1980 Olympics. Originally the Lenin Palace of Culture and Sport, it's an extraordinary structure – rotting, barred, weed-strewn and comprehensively graffitied. Heritage-listed and badly decayed as it is, it's now earmarked for restoration as a concert and convention venue, and has been recently fenced off to keep out the curious.