I can't speak for any tours except the one I was on from Akumal, but it seems likely you might be offered a stop at the Cenote Ik Kil if you are on a bus tour of Chichen Itza. You can swim in the mineral water, look at the tropical flowers, eat at the restaurant, or buy stuff at the gift shop.
MexRM - chichen itza cenote
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http://kimbriggs.com/images/mexico-riviera-maya/chichen-itza-cenote-tour/mexico-cenote-001.jpg
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http://kimbriggs.com/images/mexico-riviera-maya/chichen-itza-cenote-tour/mexico-cenote-005.jpg
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http://kimbriggs.com/images/mexico-riviera-maya/chichen-itza-cenote-tour/mexico-cenote-006.jpg
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http://kimbriggs.com/images/mexico-riviera-maya/chichen-itza-cenote-tour/mexico-cenote-007.jpg
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http://kimbriggs.com/images/mexico-riviera-maya/chichen-itza-cenote-tour/mexico-cenote-008.jpg
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http://kimbriggs.com/images/mexico-riviera-maya/chichen-itza-cenote-tour/mexico-cenote-009.jpg
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http://kimbriggs.com/images/mexico-riviera-maya/chichen-itza-cenote-tour/mexico-cenote-010.jpg
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http://kimbriggs.com/images/mexico-riviera-maya/chichen-itza-cenote-tour/mexico-cenote-011.jpg
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http://kimbriggs.com/images/mexico-riviera-maya/chichen-itza-cenote-tour/mexico-cenote-012.jpg
mexico-cenote-013.jpg
http://kimbriggs.com/images/mexico-riviera-maya/chichen-itza-cenote-tour/mexico-cenote-013.jpg
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http://kimbriggs.com/images/mexico-riviera-maya/chichen-itza-cenote-tour/mexico-cenote-014.jpg
mexico-cenote-015.jpg
http://kimbriggs.com/images/mexico-riviera-maya/chichen-itza-cenote-tour/mexico-cenote-015.jpg
These photos were taken in 2008.