From Prague to Plovdiv, engineers and architects are giving a second life to communist-built apartment blocks in Central and Eastern Europe, ready for the climate change era. One of the oldest residents of one of the tallest building in Gabrovo city, Bulgaria, is former engineer Hristo Hristov. At nearly 90 years old and "still obsessed" with how things fit together, Hristov has lived in the block since it was built three decades ago.