In between making each other nervous as hell with our respective driving styles, Arnaud and I stopped at a site known as Toniná.  The ruins here are quite amazing, predating those at Palenque by a few hundred years and only fairly recently investigated by archaeologists. Because they are fairly newly studied, there are far fewer visitors to the site and one has the sense of taking part in the discovery of the ruins.  There are also far fewer barriers to climbing all over the ruins, which is probably really bad for them but makes for great fun. We felt like we were re-enacting our own version of Raiders of the Lost Arc, climbing in and out of tight places, tunnels, up along parapets, pyramids and so on.