For such a remote site, Calakmul was surprisingly easy to get to. I had considered leaving it off our itinerary at one point thinking that it would be too time consuming and complicated to visit without a rental vehicle. We visited in August 2019 after making our way to Xpujil from Palenque by bus. 

Calakmul might be off the beaten path but it isn't unheard of and Xpujil has become a mini tourist hub for the couple dozen tourists that visit the site. It felt like most foreigners were eating at the pizzeria (with budget accommodation in the back) at the corner of the main roundabout and this place should probably be considered ground zero for getting local info for the region. We might've even been able to find someone with a rental car already but as it turned out the pizzeria knew a guy with a car that could take us to the ruins the next day at a very reasonable rate. In the end we were a group of 6 in 2 cars. 

It is a long but not unpleasant ride into the park, once off the main road the scenery is pristine wilderness and you can't help but strain your eyes searching and hoping to see some wildlife cross the road. Aside from the checkpoints there really isn't much along the way but our driver pulled off to the side around 27km in (it is unmarked and has room for maybe 3 cars) where we walked along an unmarked trail for ~45 minutes and saw howler and spider monkeys, deer, toucans, etc. We also saw another family walking the trail so it seems legit if anyone wants to enjoy the natural aspects of the park.

We were given 4 hours at the ruins and chose the long trail, climbed the 3 climbable temples, loved the views of emptiness and reminders of our experience in Tikal, had to rush the last part and finished just under 4 hours as the last of our group to return. The only downside of the day and maybe it was just the time of year, but the mosquitoes were so bad we used an entire big bottle of repellent trying to keep them off and still couldn't stop long enough to read through a whole info sign (of which there were many). We saw maybe 2 dozen other tourists there and the site is huge so you end up spread out well which can actually make following the furthest sections of the long route more confusing with a lack of coherent direction markers and nobody else to follow. 

This site is definitely worth visiting and really doesn't require a ton of effort to get to, just time. Xpujil has direct buses to Villahermosa, Campeche, Chetumal, Bacalar, Cancun, etc though the hours can be a little strange as it is all just through traffic. It would be a very long day trip by car from anywhere else and Xpujil isn't unpleasant. We had no time for it but there are other small ruins in the area as well.