General curiosity:
* As curious as a cat.
* As inquisitive as a puppy.
* As eager to learn as a sponge.
* As fascinated as a child with a new toy.
* As intrigued as a detective following a lead.
Specific types of curiosity:
* As curious about the world as a sailor exploring uncharted waters.
* As curious about the past as an archaeologist excavating ruins.
* As curious about the future as a scientist peering into a telescope.
* As curious about people as a journalist seeking a story.
The best simile will depend on the specific context and the kind of curiosity you want to emphasize.