Monterey, Carmel-By-The-Sea, and Big Sur are all filled with beautiful scenery and lend themselves to great outdoor activities. However, I was warned before my first visit that the weather is not always the best for outdoor sightseeing. I learned this the hard way when it rained all day on the Saturday I was visiting Monterey. The top option for a rainy day in Monterey is the Monterey Bay Aquarium, which is commonly listed among the top aquariums in the United States. Unfortunately, since it was a rainy Saturday, it seemed every other person who lived or was visiting Monterey decided to go to the aquarium as well.
I am a big fan of the Shedd Aquarium in Chicago, so the Monterey Bay Aquarium did not blow me away. However, it is a great place for kids, as aquariums usually are, but this one especially had smaller, hands-on exhibits that were good for capturing the attention of children beyond just staring at the animals.
I would also highly suggest buying your tickets online ahead of time, as you can skip the very long line at the door.