The light display in downtown St. Augustine is considered one of the best in the world. Naturally, it's a tourist destination from November-January every year. If you're driving, keep in mind that traffic picks up during these months.
The St. Augustine Alligator Farm is one of Florida's oldest continuously running attractions, having opened on May 20, 1893. It has 24 species of crocodilians, and also a variety of other reptiles, mammals and birds, as well as exhibits, animal performances and educational demonstrations. Plus, they serve beer!
Built in 1871 by the Spanish as watchtowers, the St. Augustine Lighthouse is one of St. Augustine's most famous attractions. You can climb to the top for a small fee! The height is totally worth it, don't listen to anything Brian says.
Built by the Spanish in St. Augustine to defend Florida and the Atlantic trade route, Castillo de San Marcos National Monument preserves the oldest masonry fortification in the continental United States and interprets more than 450 years of cultural intersections. On Saturdays, you'll find reenactments (including a canon!) in front of the fort.