Fly into Cancun. If you rent a car, you'd better be a damn good driver, it is crazy here! There is also Tulum, which is spectacular. Right now is low season here until December around Christmas, so it's a good time to be here without so many tourists. Just check the weather before you come, it is hurricane season and the weather is a bit tempermental right now
There are alot of ruins within a couple hours drive from Cancun...
I think Chichén-Itzá is about 2 1/2 - 3 hours from here...