Depending on how much driving you want to do, The Calakmul ruins in the south of the Campeche region near the Guatemala boarder are fantastic. It does take a while to get to them, as the last hour plus of driving is down a heavily potholed road through rain forest. There were lots of spider monkeys around we could hear howler monkeys, although we never managed to find them. They were so much more worth visiting than Chichen Itza, which even at 9am was packed with tourists and countless little stands selling souvenirs. You can climb the pyramids in Calakmul too, which offers views of, um, tops of trees
