Things to do in Cozumel.

The Ultramar and Winjet passenger ferries from Playa del Carmen run every 1-2 hours and take ~45 minutes (USD $20-25 each way). For drivers, there is a car ferry from Calica (south of Playa) — much slower and pricier. From Cancún, the fastest path is the ferry through Playa del Carmen; total transit ~2.5 hours.

Mr. Sancho's, Nachi Cocom, and Paradise Beach are the three best-known all-day passes (USD $50-90, food and drinks included). They sit on the leeward (west) coast — the protected side with calm water and reefs offshore. The east coast has empty beaches and rougher water; pick the leeward side unless you want a wild swim.

Palancar reef on the southwest coast is the postcard — drop-off snorkeling over a coral wall. El Cielo (a sandbar covered in starfish) is shallow and family-friendly. Most snorkel tours hit 3 reefs in one trip; book directly with the local marina operators rather than through cruise-ship sellers.

Most tourists rent a scooter or jeep for a day (USD $35-60) and drive the island perimeter loop — about 90 minutes if you stop nowhere. Taxis work in San Miguel but charge a "tourist rate" that's 2-3x what locals pay. Public buses do not exist beyond a few in-town routes.

One day from a cruise ship gets you one beach club OR one reef tour, not both. Two days lets you do both plus dive the Palancar wall. Three days is the sweet spot if you're flying in — you can hit all three coasts and at least one cenote without rushing.