Full disclosure--I worked here as a volunteer for four plus years, and had a good time with the fishes and other creatures. The Monterey Bay Aquarium is on the site of the former Hovden Cannery on Steinbeck's Cannery Row (between Pacific Grove and Monterey) along the shoreline.
Parking for this place is very problematic so I'd recommend spending a few bucks and heading for the city-owned garage a block away, rather than looking for on-street places, which are all metered anyway. Once there be prepared for a hefty admission fee. But the place is one of the few in the world where the water comes directly from the Ocean with limited plankton removal during the day, and no other filtration. There's even a million gallon seawater tank in the Outer Bay exhibit with a massive plexiglass window to watch the fishes head by.
Founded with the generous assistance of David Packard (co-founder of HP), the Aquarium has doubled in size since it opened and is listed as one of the most family friendly places to visit in the US. It was used as a fictional aquarium in Star Trek IV, the Voyage Home (1986), for all you trivia hounds out there. It is first and foremost an educational facility, with an emphasis on the Monterey Bay itself.
The Monterey Marriott offers combination stay and go there packages from time to time. And in an ironic twist, the Aquarium has an excellent restaurant 'perched' above the bay, which offers several excellent seafood entrees. Not from the tanks I am quick to add.
One postscript: When I signed on as a volunteer I needed to fork over twenty dollars for the textbook I needed on Marine Biology, attend lectures for 14 weeks, pass 14 test, complete an actual on-site experience with an Aquarium paid worker posing as a guest, and be evaluated later! Not for the faint of heart--our shift included a retired Admiral and several M.D.s, also retired. We got the full learn it or else treatment!
Worth a visit when in Monterey.
PS I took these on my most recent visit there. The Moon Jelly exhibit is spectacular!