Crystal Palace was a one of a kind structure built for The Great Exhibition in 1851 in Hyde Park. For the first time people could have a glance of the future made of glass and metal. After the exhibition the Palace was moved to South London, where it was a very popular place to visit. I assume it would still be a great attraction if it did not burn down in 1936.
However the Crystal Palace Park itself is still very nice with several interesting places, like the Dinosaur Park with quite unusual take on the creatures.