December to March is when Isla Mujeres is at its most clement. But, if swimming with whale sharks is your MO, time your trip to their migration schedule (June to September).
Getting there
Planes
Cancun International Airport is the closest to the island, around a 30-minute drive from Marina Hacienda del Mar where you can catch a boat for the next leg of the journey.
Boats
Sailing from Marina Hacienda del Mar will take around 40 minutes in a regular boat, but book a speedboat and you’ll cut that in half.
Automobiles
You’re unlikely to need a car on the island – bikes should suffice.