If you're already SCUBA-certified, you're in luck; Cancun has plenty of outfitters ready to rent equipment to you and your partner so you can explore the deep blue sea together. If you're not certified, many Cancun operators offer basic, introductory courses that get you in and underwater quickly. Expect to see coral reefs and diverse animal life; Cancun also has three shipwrecks that are accessible to divers. While diving with an instructor-guide and other vacationers can be fun, diving with your partner is even better. Look for PADI-certified shops with bilingual staff.