These 4 gas holders, known as gasometer were built in 1896 as part of the gasworks at Simmering. After they were closed down, the 4 historic towers were renovated, converted into apartments, shopping malls and offices and reopened in 2001. When they were built, the gasometers were the largest in Europe. They are listed by the country’s heritage ministry as outstanding examples of industrial architecture. The renovation goal was to reuse the external façades of the existing buildings, avoiding total demolition of the building and minimizing the generation of demolition waste. The gigantic size of this construction project is illustrated by the fact that Vienna's Giant Ferris Wheel would easily fit into each of the four 75-metre high gasometers.