Collect rental car or take a private shuttle/ADO bus to Tulum (about 1.5–2 hours). This gets you into town with time to settle and beat late-afternoon traffic.
Iconic white-sand public beach with turquoise water and beach clubs nearby — perfect first afternoon swim and sunset photos (public access; clubs have fees).
Climb the Nohoch Mul pyramid (if open) and rent a bike to explore the expansive site; the ruins are open roughly 8:00am–5:00pm and less crowded in the morning.
Short drive south (~25–30 minutes) to the Akumal bay area, known for sea turtle snorkeling; arrive early to avoid crowds and for better sea conditions.
Join a guided snorkeling tour or rent snorkel gear to swim with sea turtles and colorful reef fish; morning departures are best and many operators run tours 8:00am–11:00am.
Book a morning beach club day pass (La Zebra / Papaya Playa) or a beachfront yoga class to stretch and soak up the last tropical hours (beach clubs typically open by 9:00–10:00am).
Allow ~1.5–2 hours to return to Cancun depending on time of day; target arriving 2–3 hours before international flights or 90 minutes before domestic flights.