From the top of one of the tall structures in Calakmul, you should be able to see El Mirador on a clear day, possibly with binoculars. El Mirador is on the Guat

From the top of one of the tall structures in Calakmul, you should be able to see El Mirador on a clear day, possibly with binoculars. El Mirador is on the Guatemalan side and is also a pretty amazing site, especially if you want to see what some of these sites look like before they are fully excavated and cleaned up for tourist crowds. El Mirador is deep in the jungle and requires a multi-day journey, preferably with mules to get there. When I went several years ago, I remember only crossing paths with one other group of tourists for the whole 60 mile round trip journey.