Tulum itself is a treasure to explore, relax on the white sand beach, or snorkel in the turquoise water. There are the famous ruins of the Mayan city Chichen Itza located about 1 1/2 hours away, served by many tour operators. We highly recommend you plan a day in the Sian Ka'an biosphere. It is an expansive, beautiful, protected area that covers miles and miles of lagoon, beach, and mangrove. You will be blown away by the variety of birds, fish, dolphin, and other wildlife. Nearby there are dive shops, kite surfing shops, and places to rent kayaks or paddleboards.
Along the beach road you will find many cool restaurants, including Hartwood (Google if you haven't already heard how amazing it is), Posada Margherita (best Italian date spot ever), or Casa Banana for great Argentine meats. Visit Coqui Coqui (besides being absolutely beautiful, they sell handmade perfume).
In town you will also find a plethora of fun spots and unique experiences. Asadero is a great dinner option when you crave an open flame steak. For margaritas made from freshly ground cane sugar, head to Batey's. Azafran offers a delicious German breakfast. Prices in town are much cheaper than on the beach and give you a feeling of the local cultural experience.