While visiting Tallinn for a conference in 2011, I nipped out for a quick trudge around Linnahall, the largely disused concert/leisure venue built as a kind of nautical extension of the 1980 Moscow Olympic Games. Now only used as a heliport to Helsinki and dock for catamarans, much of the megastructure is derelict, though open and appealing in its own way. The architects were Raine Karp and Riina Altmäe.