The ancient Mayan palace and compound of Chichen-Itza dates back to the year 800 AD. The palace is remarkably intact, and an entire day can be spent wandering the grounds. When we were there, they still allowed climbing the pyramid, which was the single most terrifying event of my life. After the hands-and-knees crawl to the top, the only way down (other than falling off the cliff-like side) was to bump down the steps on your butt, feeling with your feet for the next narrow (I'm talking like 6 inches deep) step and hoping you wouldn't slip on the lichen growing on them or put your hand right onto a tarantula. We both made it, but what a RUSH! We had great views of the Mexican jungle.
Other than that, it was fun to explore the old ruins, mostly covered by jungle and not yet renovated. Be careful: there are quite a few deadly snakes around, so watch where you step. After your hard day, have a Corona and pizza at the National Park nearby—lunch with two beers each for two people was less than $4. Skip the pricier souvenirs there and drive 10 minutes to Piste, where street vendors will chase you down with handmade treasures. We bought a really cool carved jaguar head, a wall mask, and some other assorted novelties for about $20. Driving in Mexico felt easy and safe, and everyone we encountered was friendly and helpful.