What does one have to see in Cancun?

I need some kind of advice, or some suggestion. What does one have to see in Cancun? I am going to Cancun. But I must say that it is not the place where I wanted to go. But because of my financial situation, it is the one of the few places that I can afford. So, I really need some guidance where I can go, and what I can see there.

I was in Cancun. But I really dont understand why you are so negative about this place. Some people dont have enough money to go anywhere, so you can at least travel and get to know some new place. There are some interesting places that you can visit. There are a few nice historical monuments. One is from very far past. But I like it very much. It is the Pyramid of Kukulcan ( I think that the spelling is correct, but I am not sure). I really like it. I have always wanted to see some pyramid with my own eyes. It is 1000 years old (couple years more or less) and it has more than 350 stairs. So I warmly suggest you to visit this place.