Emerging somewhat bleary eyed from the overnight bus journey – although we both slept better than we thought we would – and blinking in the morning sun, the crisp freshness of the mountain air strikes us immediately. After several stays in humid locations over the last few weeks, culminating in the cloying air of Palenque, it feels like a completely different climate here. We are some 2,100 metres higher above sea level than we were in Palenque and it is instantly noticeably different. This is San Cristobal de las Casas, where evenings will be chilly and, if all goes according to plan, virtually the last point at which we feel…