FYI - with current local taxi rates it's 450 pesos or $45 USD(depending on how you pay) for a
one way trip from Desire RM into Cancun centro or the Cancun Hotel Zone (about a 30min ride depending on time of day/traffic).
You can book private tours for anything with one of this
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You can book public(shared) tours right from the activity desk when you arrive at Desire RM
However, IMHO, why pay the top $$ to be at Desire and then go away from the action on an excursion - next time you come down book and stay in a cheaper place in the Hotel Zone for a day or two - do excursions/tours and then finish your real vacation at Desire