This 22 m² Barcelona apartment used to be a service room, where the water tanks were stored. But that was before Christian Schallert, its present owner, and architect Barbara Appolloni took on the project. Now it is a fully functional pad, smart, versatile and very stylish. Complete with the little terrace – the space can be transformed into several rooms – bedroom, kitchen, dining room, office. All thanks to clever storing solutions, hidden in walls. Christian calls it ‘an active apartment’ and claims that these daily space-transforming ‘exercises’ keep him in shape. Another hidden bonus of living small…