The Mayan ruins in Tulum are right on the coast, about a 10 minute drive from downtown. Tours are available but not necessary. You can hire one of the local guides to learn more about the history if you choose to explore with a guide! Visit early in the morning to avoid crowds. Head down to the beach after to cool off in the ocean!
The cenotes of Tulum are a series of crystalline freshwater pools connected by a maze of underground rivers. There are quite a few cenotes surrounding Tulum. Consider going earlier in the day to avoid crowds and bring cash for the entrance fee and snorkel gear! Riviera Maya is filled with cenotes! Many offer swimming, snorkeling, cliff jumping and diving. Check out The Culture Trips's Guide to Exploring the Cenotes In and Around Tulum: https://theculturetrip.com/north-america/mexico/articles/a-guide-to-exploring-the-cenotes-in-and-around-tulum/
A UNESCO world heritage site, Sian Ka'an is a protected biosphere about one hour south of Tulum. Home to dolphins, marine turtles and up to 500 species of fish, the Mesoamerican Reef is second only to the Great Barrier Reef in size. Go swimming, paddle boarding and snorkeling. Head to Kaan Luum Lagoon for some amazing crystal clear water.
Spend the day at Casa Malca! Pablo Escobar's former mansion that was turned into a boutique hotel by a New York art dealer. He filled the place with valuable pieces from his art collection. You can explore the property and spend the day at their beautiful beach club!
The Mayan Clay Spa is located on the jungle side of the Tulum beach road and specializes in detoxing clay massage treatments, using all natural Mayan Clay products. Spa treatments can be reserved for 60 minutes, 90 minutes or 2 hours for both individuals and couples. This is one of the more reasonably priced spa options in Tulum.
There are tons of beach clubs along the coast. Some clubs charge a small fee for use of the cabanas/day beds, but most just ask for a food & drink purchase. Taboo has a clean beach area with ample multilevel decks, a dozen wooden cabanas, a Mediterranean restaurant, cocktails and most importantly -- a DJ playing music all day long!