Pic from 'Candela: Shell Builder,' by Colin Faber
The intersecting hyperparabaloids of Felix Candela's restaurant at Xochimilco, Mexico City. You can see from the diagram above how the structure is formed from the 'saddle' shape of the 'hypars.'
The 'hypar' structure means the seemingly complex curves can all be constructed using straight lines, as the diagram above also helps to demonstrate.
Candela's ingenuity here means the visible 'free edges' of the concrete shell are as thin as just forty millimetres.