The reef here is superb, but Tulum ’s diving claim to fame is the slew of freshwater cenotes  and caves, all within easy reach. Divers with open-water certification can make “cavern” dives, defined as no more than 30 feet deep or 130 feet from an air pocket. (Full-cave diving requires advanced training and certification.)
If you haven’t dived in a while, definitely warm up with a few open-water dives before your first cenote trip. Pay particular attention to buoyancy control, which is especially important in cavern environments and is complicated by the fact that it’s freshwater, not saltwater, and typically requires one or even two wetsuits (and corresponding weights plus a flashlight).
Prices for cenote diving are fairly uniform from shop to shop, around US$110–150 for two tanks, including transportation, entrance fees, and sometimes equipment. (If not, a full kit costs around US$15–20 per day.) Tulum’s shops also offer multidive packages, cave and cavern certification courses, and reef and snorkeling trips. As always, choose a shop and guide you feel comfortable with, not necessarily the least-expensive one.
Halocline Dive Center (Calle Andrómeda btwn Calles Orion and Centauro, tel. 984/120-6402, www.halocline-diving.com , 8:30 a.m.–7 p.m. daily) is a friendly, low-key shop with good prices and even better gear, thanks to being certified in equipment maintenance.
Aptly named for the Maya underworld, Xibalba Dive Center (Calle Andrómeda btwn Calles Libra and Geminis, tel. 984/871-2953, www.xibalbadivecenter.com , 9 a.m.–7 p.m. daily) specializes in cave and cenote diving. The shop has a good reputation for safety and professionalism.
Cenote Dive Center (Calle Centauro at Calle Andrómeda, cell. tel. 984/871-2232, www.cenotedive.com , 8 a.m.–4 p.m. Sun.–Fri.) also specializes in cave (US$865) and cavern (US$375) certification courses and fun dives.
In the Zona Hotelera, Mexi-Divers (Carr. Tulum–Punta Allen Km. 5, tel. 984/807-8805, www.mexidivers.com , 8:30 a.m.–5 p.m. daily) is located opposite Zamas Hotel in the Punta Piedra area and has ocean snorkeling and diving trips twice daily at 9 a.m. and 1 p.m.
A short distance north of Tulum, Hidden Worlds Cenotes Park (Hwy. 307 btwn Tulum and Akumal, cell. tel. 984/120-1977, www.hiddenworlds.com , 9 a.m.–5 p.m. daily) has excellent, if sometimes crowded, dive trips in the semiprivate cenote system right at its shop.
Like divers, snorkelers have an embarrassment of riches in Tulum , with great reef snorkeling and easy access to the eerie beauty of the area’s many cenotes. Dive shops listed here offer snorkel trips of both sorts; reef trips cost US$25–30 for a 2.5-hour trip visiting 2–3 different spots, while cenote trips run US$40–50. Hidden Worlds and Dos Ojos , both north of Tulum, offer an easy and rewarding introduction to cenotes, offering guided snorkeling tours through spectacular caverns several times daily.
To rent snorkel gear, stop at any of the dive shops in town or ask at water sports outfits along the beach.
Extreme Control (Playa El Paraíso Beach Club, Carr. Tulum–Punta Allen, 2 kilometers/1.2 miles north of junction, cell. tel. 984/745-4555, www.extremecontrol.net , 9 a.m.–sunset daily) is Tulum’s longest-operating kiteboarding outfit, offering courses and rentals for all experience levels and in various languages. It also organizes extended kiteboarding tours in the northern Yucatán as well as Isla Holbox 
In Tulum, instruction typically takes place at Playa El Paraíso Beach Club , north of the junction. Private classes are US$72 per hour, or US$216–432 for three-to-six-hour introductory packages, including equipment. Group classes are somewhat less, and there’s a discount on additional instruction for those who complete a package. Open December–May; by appointment only the rest of the year.
Based out of Playa Azul Tulum Hotel, Morph Kiteboarding (Carr. Tulum–Punta Allen Km. 8, cell. tel. 984/114-9524, www.morphkiteboarding.com ) offers classes by IKO-certified instructors to all levels of kiteboarders. Rates are for private classes, though group lessons can be arranged as well: US$225, US$395, and US$550 for three-, six-, and nine-hour courses, respectively. Equipment rental is available, including for those wanting to kite independently (IKO Level 3 certification required). Hotel and kiteboarding/diving packages also can be arranged—check the website for specials.
Stand up paddling, or SUP, is all the rage these days, combining the scenic qualities of kayaking with the thrill and challenge of surfing. The Riviera Maya  is well suited to the sport, with moderate surf and crystal-clear water. (You can see a surprising amount of sealife doing SUP instead of kayaking, thanks simply to the improved vantage point.)
Ocean Pro Kite (Akiin Beach Club, Carr. Tulum–Punta Allen Km. 9.5, cell. tel. 984/119-0328, www.oceanprokite.com ) offers SUP lessons for all levels, starting with safety and theory on the beach, graduating to kneeling paddling, then standing and catching waves. Private classes are US$60 per hour or US$120 half day, while groups of two or three start at US$40 per person per hour. Gear, guide, transport, and refreshments all included.
Snorkel in the ocean, snuba in a lagoon, float down a river, or swim with dolphins at Xel-Há (Hwy. 307, 9 kilometers/5.6 miles north of Tulum, tel. 984/105-6981, www.xel-ha.com , 8:30 a.m.–6 p.m. daily, US$89/59 adult/child all-inclusive). Children and beginner snorkelers often list this as a highlight of their trip, while the more experienced may find the waters overrun with tourists and underpopulated by fish. Dolphin interaction programs cost extra, too (US$109–159 pp).
Along with renting well-maintained bicycles, Iguana Bike Shop (Av. Satélite near Calle Andromeda, tel. 984/871-2357, www.iguanabike.com , 9 a.m.–7 p.m. Mon.–Sat.) offers mountain bike tours to snorkeling sites at various cenotes and beaches, as well as turtle nesting grounds on Xcacel beach . Prices vary depending on the tour; they typically last four hours and are limited to six cyclists.
A holistic spa set over the beach at Copal hotel, Maya Spa Wellness Center (Carr. Tulum–Punta Allen Km. 5, tel. 984/807-9522, www.maya-spa.com , 8 a.m.–8 p.m. daily) offers a variety of massages, body wraps, and spiritual treatments like Reiki and Maya crystal therapy. There’s also a free public yoga class every morning at 7:30 a.m.
Located at the Ana y José hotel, Om…Spa (Carr. Tulum–Punta Allen, 3.5 kilometers/2.2 miles south of junction, tel. 998/880-5629, www.anayjose.com , 10 a.m.–6 p.m. daily) is a full-service spa set in an chic beachfront setting. Choose from a menu of massages (US$85–100) and body treatments (US$60–100); ask about the Yumka Chocolate Spa (US$150, 120 minutes), which includes a cacao body mask, chocolate facial, and a chocolate foaming bath.
Surrounded by lush vegetation, Yoga Shala Tulum (Carr. Tulum–Punta Allen Km. 4.4, tel. 984/157-5101, www.yogashalatulum.com , 7:30 a.m.–9 p.m. Mon.–Sat.) offers a wide range of yoga instruction, plus Pilates and meditation, in its gorgeous open-air studio. Classes cost US$10 each or US$50 per week. There also is an affordable hotel on-site. Look for both on the inland side of the Zona Hotelera road.