Don’t expect the wide open, clean beaches you’ve seen in other Caribbean destinations. A few hotels on Ambergris Caye [1] have nice soft, white sand (some natural, others dredged from the lagoon side, an ecologically questionable activity); most only have short strips of sand and seagrass shallows.
But even if the “beach” serves as a pedestrian walkway and an open market in most of San Pedro, the ocean is as beautiful as ever, and small docks and pools give access where swimming might otherwise be difficult. One of the better natural swimming and snorkeling beaches is 12 miles north of San Pedro at Tranquility Bay Resort.
After Hol Chan Marine Reserve [2] and Bacalar Chico National Park and Marine Reserve [3], most of the other noteworthy sights in the area are under water (please see the Turneffe Island [4] and Lighthouse Caye [5] dive sights section). Every dive and snorkel operator has his own list of secret spots to take you.
For many, the main attractions of Ambergris include the shops and boutiques [6] in central San Pedro and the chain of resorts stretching north and south from the island. Walking, biking, or golf-carting in either direction can be a great half- or full-day activity, as you hop from one swanky hotel bar to the next, sampling different cuisines, moods, and color schemes, all with a view of the reef just offshore.
Links:
[1] http://www.moon.com/destinations/belize/the-northern-cayes/san-pedro-and-ambergris-caye
[2] http://www.moon.com/destinations/belize/the-northern-cayes/san-pedro-and-ambergris-caye/sights/hol-chan-marine-reserve
[3] http://www.moon.com/destinations/belize/the-northern-cayes/san-pedro-and-ambergris-caye/sights/bacalar-chico-marine-reserve
[4] http://www.moon.com/destinations/belize/the-northern-cayes/turneffe-islands-atoll
[5] http://www.moon.com/destinations/belize/the-northern-cayes/lighthouse-reef-atoll
[6] http://www.moon.com/destinations/belize/the-northern-cayes/san-pedro-and-ambergris-caye/shopping