We went to Chichen Itza via
DCL. It is a lengthy excursion because it requires a ferry ride between Cozumel and the mainland, then a few hours drive to Chichen Itza. But it's a great excursion just to be able to see that historic site. It is not exhausting physically in any way. Just a moderate length walk from the parking lot to the pyramid area, which is a flat, visitor-friendly area (and of course there are other historic structures on the grounds around the pyramid). One thing to keep in mind is the importance of bringing an umbrella in case it rains. The excursion company will not provide those for you.
A DCL excursion was the only way I wanted to do Chichen Itza, because it takes you so far from the ship. I wanted no worries about being able to get back on board in case of a delay.