I visited this WHS in December 2015. Some say that it's all about the journey, not the destination. To me Calakmul truly deserves it's place on the list and is a very good example of how a mixed WHS should be. You won't end up in Calakmul by chance. The Mayan ruins are in the middle of the biosphere reserve on the forest border with Guatemala. I'd suggest getting to the Rio Bec Mayan cluster close to Chicanna/Becan/Xpuhil and visiting these ruins first and sleeping over to visit Calakmul first thing in the morning. I marvelled at House of the Serpent Mouth in Chicanna and spent a lovely afternoon exploring practically alone for hours on end. I was at the entrance to the 70km road to the site at around 07:30 and it turned out to be a wise choice. The road is full of potholes and turns and quite narrow at times to be a 2 way road. Being there early meant I could drive on without having to slow down because of other vehicles in the opposite direction (which I experienced on my way out!). The highlight of the ruins are the several carved stelae beneath the 'pyramids'. Climbing to the top is still allowed and it's a great experience to be high above the forest canopy and have a panoramic view of the biosphere. The peak of the recently discovered El Mirador in Guatemala can be seen on a sunny day and with binoculars. Structure 2 is one of the tallest Mayan ruins in Mexico and a small tip to help you climb up and down safely is to go up and down in a zig zag pattern not straight up and especially not straight down. There's no rope to help you like there is in Coba for example but the view is certainly worth the effort and to me the best forest view you can get from any Mayan ruin in Mexico. The biosphere is full of interesting birdlife and lots of elusive fauna. The loud howler monkeys echo all over the place and can be easily spotted while the quick black handed spider monkeys are a bit more difficult to capture on camera! All in all this is one of my favourite Mayan sites mostly because it's more quiet than other more iconic Mayan ruins and because they can still be enjoyed to the full.