Even if you're only enjoying a week's all-inclusive vacation in Cancun or the Mayan Riviera, consider making time to explore Mexico's rich history and committing to a trip to the immensely interesting Chichen Itza.
You might notice, however, that there are exclusion barriers and other means of keeping visitors from actually touching the pyramids themselves. As @Holly mentioned in another thread, there are more than 100 pyramids in Mexico and some of them permit more freedoms than others.
Teotihuacan, the Pyramid of the Sun
Another great set of pyramids located just outside of Mexico City are still very accessible to visitors at Teotihuacan, the Pyramid of the Sun. There was an archaeological dig underway when I visited in 2017!
It's a short drive out of the city, better to be arranged in advance with a private car and driver or with a recognized tour group.
Interestingly, the top levels of the lower pyramid was destroyed during excavation by an earlier archaeological effort - they used explosives!!!
For the extravagant, try a hot air balloon ride over the pyramids with limited pick up from Mexico City
For the everyday, try a private tour with an archaeologist from Mexico City
The pyramids at Coba, for example. These aren't as well preserved as the site at Chichen Itza, perhaps it is because of this and the reduced foot traffic that allows them to remain open for climbing.
Here's a throwback to one of my own visits to Mexico in 2009 and a short climb up the stairs at Coba
And where it's located on Google Maps
An idea of the cost for a private day trip from Tulum or Playa del Carmen
An idea of the cost for a private day trip from Cancun including Chichen Itza and cenote