One of his earliest projects was the charming Penguin Pool at London Zoo. Concrete was just becoming fashionable in 1933 and although architects loved the material, Arup noted that they didn't necessarily know how to use it correctly.
Working with the Russian architect Berthold Lubetkin, he created these concrete ramps that intersect over a pool for the penguins to march up and down, to the delight of children and adults. The ramps are thin walkways made of reinforced concrete. The design was admired for its technical virtuosity and established Arup's reputation.
The penguins have moved to another pool, but the structure remains.