Fun stuff to do in Mazatlan?

We're in Mazatlan from 9am to 6pm on January 24th (from the Carnival Cruise), what should we do in town?

We're 26, and we were looking for something unique that we can't do at home. We live in a touristy beach town, so sunbathing and shopping are not on the to do list. We'd like to do something more active, like snorkeling, horseback riding, etc, or something unique to the area.

There are several tours that you can look in to: Tequila factory, stone island, city tour, country tour. Most of the time you have to book these the day before and pay attention to what time they will have you back. The city tour is the shortest and fairly informative. Or, you can take a cab or a pulmonia (those golf cart looking things) and ask to go to the cathedral. There is this beautiful Catholic cathedral and within walking distance there are several quaint shops and restaurants in the town square (Muchacha square), this area resembles New Orleans a bit the way it is set up. Then catch a ride back, that way you are on your own schedule.

That sort of depends on what you consider fun! Para sailing,horseback rides,water park, Old Town Mazatlan, shopping, strolling the beaches, stone island? There is not a lot you can do in such a short time, and during the daytime. Cliff divers, pool hopping? Central market? A bit more details please.

You will be here the week before carnaval so will see alot of preparations for that. The cathedral and opera house are in the same area and you could lunch on Plazuela Machado. Also around there you will find some great little artisian shops. Hiking up to the lighthouse gives you some great views (highest working lighthouse in the world) If you want to tour some neighboring villages, the Concordia/Coppala tour is nice, as is El Quelite. Snorkeling here is fair at best. Horseback riding can be done at either Stone Island or Playa Bruja. Have fun!