I have been to both Chicken Itza and Tulum on various trips to Mexico. Chichen Itza is a must see. Unbelievably wonderful. We went five years ago. We were able to climb outside as well as visit inside on our trip. Also, we hired a local guide there to explain elements. It was helpful to us. He walked us to a cenote there on site. I don't recall it being a long walk. You will probably want to rent a car in place of a taxi. It was a wonderful experience! Tulum is lovely, though does not compare. I know nothing about Uxmal.