This strange looking object is Gaudi's model of the building loads and stresses of the Sagrada Familia. It works on some kind of upside down gravity principle with little weighted bags.
"The technique Gaudí used to design the church was to hang little bags of birdshot from chains. Gravity would pull these bags downwards, giving even weight distribution and stretching the chains to form a model structure, thus showing him the shapes and angles his pillars would need to be. By using a mirror placed under the model, Gaudí could then see the model as it should look. The model looks dated; however, this would allow Gaudí to perform designs only computers could do today. It put him a good 75 years ahead of the designs of the time.."
"The profiles of the towers and arches are catenary curves. They pass all their weight down to their own foundations, and the structure stands alone without buttresses. Gaudí was no lover of mathematics, and to avoid having to solve cubic equations he made upside-down string models, hanging bags of lead weights from the strings to represent the load the arches and vaults would later bear, and then copied the curves of the strings."