What is it? Dolphin and whale watching (Captain Dave's Dolphin Safari)
Where is it? Dana Point, in Orange County
How far from Disneyland? About 40 minutes
How much? ~$50 per person for a 2-3 hour sailing
There are probably literally dozens of dolphin/whale watching companies all up and down the coast, but I've only used one, so that's the one you're going to hear about! We used Captain Dave's, which is in Orange County not terribly far from Disneyland. It was amazing! There were literally hundreds of dolphins in the waters around us! Plus, there were two features on this boat that made the trip extra special. One, there was an area where the floor was nylon netting and you could actually lay down with just the net between you and the dolphins a couple of feet away swimming next to the hulls.
Then, the bottoms of the two hulls had glass panels in the walls so you could be under the water with the dolphins swimming right next to you.
You also get what I bet is pretty reliable viewing of California sea lions. They like to hang out on the buoys:
We didn't see any whales, but it wasn't supposed to be a particularly good time for that and we were satisfied seeing the dolphins. This company has a
little chart that tells you when is a good time to see what and they keep a
log of sightings on their trips. Some of the counts are absurdly specific: one I just saw said 1,876 common dolphins (did they really count to 1,876?), but the count for my trip seems spot-on. I don't think they're padding their stats.