Simple and Direct:
* As adventurous as a mountain climber scaling a sheer cliff.
* As adventurous as a sailor charting uncharted waters.
* As adventurous as a wild animal exploring new territory.
Figurative and Evocative:
* As adventurous as a butterfly flitting from flower to flower, seeking new nectar.
* As adventurous as a river carving its own path through the landscape.
* As adventurous as a dream taking flight, soaring to new heights.
Humorous and Playful:
* As adventurous as a squirrel raiding a bird feeder.
* As adventurous as a child exploring the back of the refrigerator.
* As adventurous as a dog chasing a butterfly in a field of flowers.
Ultimately, the best simile for "adventurous" will depend on the specific context and what you want to emphasize.