Palenque ruins are one of the most impressive ruins I visited in my entire life. They are in the middle of the jungle but easily found by a small road, about 10 kilometers from the tiny center of Palenque. You can hire a guide which I highly recommend to get a sense of the prehispanic Mayan culture and understand the way of living of this fascinating population since there are no explanations on the site. It costs about 3$ to get in per person. You can also choose to do a day tour which includes the ruins, a walk through the jungle and a bath into hidden waterfalls.