This egg was inspired by Faberge's visits to the United States in the late 19th century (during which time Americans had invented mechanical carousels that people paid to ride on in fair grounds).
The egg itself is made of gold, with blue and red enamel coating the outside, and is decorated with silver horses. At the top of the egg is a miniature replica of the Imperial Russian crown.
When you open the egg, you see the surprise: a carousel of horses made of painted enamel. It's a fully working toy. If you wind it up, the carousel begins to spin, music begins to play and the tiny horses move up and down just as in a real carousel. Faberge's genius was that he was a jeweller, an artist and an engineer all at once.
Here's a close up of the carousel: