The Marine Mammal Center located in the Marin Headlands in Sausalito is made up of an amazing group of people doing amazing things.
They rescue seals and sea lions (yes, there is a difference!) along the Northern California coastline. Most of the animals there are in the "hospital" because of things humans do to them, and also because of occasional shark bite or two.
I recommend a visit to the Marine Mammal Center to learn more about the ocean environment and how humans effect the animals that live there. Better yet, volunteer there!
They have an outreach program for schools and you can tour the facilities as well. The animals are in view and you can hear (and smell) them! There's also a gift shop and very nice beach (Rodeo Beach) nearby.