This is a list I put together for someone asking about activities in/near Tulum. All driving times are from Milamores, which is at the end of the hotel strip, very close to Si'an Kaan.
There are many activities to choose from:
Tulum ruins ($7/peson or $15 with tour) takes about two hours to tour the ruins,
15 minute drive from Mil Amores
Tulum - Wikipedia, the free encyclopedia Kayaking in Sian Ka'an
$50/person, half day tour, 15 minute drive from Mil Amores
Kayaking Snorkel or dive in a cenote (Bel-Ha)
depending on gear, free-$80/person, 5 minute walk from Mil Amores
Cenotes: Riviera Maya, Quintana Roo, Mexico Daytrip to Coba:
1 hour away, $5/person or $20 with tour, bike rentals $10/person
Coba - Wikipedia, the free encyclopedia Snorkeling in Soliman Bay
20 minutes away, $5/person snorkel rental
Soliman Bay, Tankah Bay Mexico Cataman ride including lunch & snorkeling
30 minutes away, $50/person
Akumal Mexico tour: Sailing & Fishing: Catamaran Kantaris Zipline and Snorkel Hidden Worlds Cenote System
20 minutes from Mil Amores and half day experience, $50/person
Zipline Cenote Adventure ...but best of all is the beach
Why I want to go back. on Flickr - Photo Sharing!