Here are some of the most striking chimneys and ventilation shafts to grace a Barcelona roofline, on Casa Mila or "La Pedrera", one of Gaudi's most famous apartment buildings (so famous that you need to get there for opening time or be swamped by the deluge of tour parties and other visitors).
They look vaguely like Dr. Who's latest adversaries - though how many of them are decorated with fragments of broken plates and champagne bottles?. The humanoid appearance is hardly surprising, since his designs are heavily influenced by organic forms: to the point that (if I understood the exhibitions inside correctly) he did not produce fully worked out plans, rather sketches and concepts, influenced by his observations and studies of trees, shells, animal skeletons and so on.
The tour stars on the roof, and then you descend to the attic where all this is explained (there's a similar though, as I recall, less exhaustive explanation of all this at his other great creation across the street, the "gingerbread house" Casa Batlló). Much is made of the "catenary arch", the inverted shape of a suspended chain: turn the image of the chain model in this picture upside down, and you have the outline of the structure for one of his churches, complete with its supports, struts and buttresses. And looking the length of the attic, with a succession of arches supporting a single beam is like being in the belly of a whale.
Once you get down to the apartment on show, it all becomes much more conventional, since the (admittedly flexible and flowing) spaces are organised and decorated much more to the tastes of the early twentieth century. What sticks in the mind is the extraordinariness of what's on the roof, as striking a contrast to today's bland office-boxes as it is to the pomposities of its predecessors.