Many are of the opinion that Chichen Itza is too far a drive to make from Playa Del Carmen.  Unfortunately, the ruins at Chichen Itza are an ABSOLUTE must see....but fortunately for you, this will outline an excellent day trip away from the cozy confines of your Playa Del Carmen hotel.

First, you must rent a car.  This trip is all about packing in as much as you can into one day, and you sure as heck won't be able to do that being held hostage by a tour operator.  Now, there are 2 basic routes from PDC to Chichen Itza.  There is a toll road (Cuota) that can be had by heading north towards Cancun, and then there is a "back road" (libre) that is connected to by heading south to Tulum from PDC.  Try to get to Chichen Itza as EARLY as possible and you can do this by taking the toll road (which is really just a highway for the Yucatan), you can use the "libre" road on the way back since it is way more scenic.  Anyway, set your alarm clocks for 5:30 and try to be out the door by 6 am. Don't cringe as you glance at that previous statement, but you will thank yourself later for waking up bright and early.  Head north on Higway 307 back towards Cancun Airport.  You will spot an exit that reads HWY 180-D and will also say "Chichen Itza" RIGHT BEFORE the exit to the airport.  There will also be a McDonalds there, so this might be a good time to stop in thru the drive thru and maybe grab some oj, coffee, and yogurt or something and also fill up on gas if you haven't done so already.  So exit from 307 onto this highway that will take you out to HWY 180-D.  Once you get onto this highway, you will notice speeds start to increase.  At first, you will be hesitant to step on the gas for fear of speed traps....but then soon realize, that at 6:30 AM, you are only car out here...and now entering what is amounting to "the boonies"; so there was definitely no cops out there because it would be a complete waste of time for them to nab a speeding car when they only come by once every 10-15 minutes or so.  No joke.  Anyway, this highway will connect you across to HWY 180-D.  Once you get to the HWY 180-D intersection, follow the signs that say Chichen Itza and the road will merge into HWY 180-D heading in the right direction (west).  You will be on this road for a while.  There will only be 2 stops on this road and the only thing you will see on the highway is jungle and the occasional Mexican villager on his bike.  To reiterate, seeing other cars at this early in the morning is rare. The two stops will be:  1) a toll right before you get to Vallodolid (~$15),  2) a gas station about 30 km past Vallodolid (be sure to fill up here if you are running low).  After the gas station, a few more km down, you will find another toll that you must pay (~$5) and subsequently exit the highway right after.  You will notice the signs for Chichen Itza and Piste (the neighboring town).  Heading south on this exit from HWY 180-D, you will drive for about 5 minutes before reaching the small village of Piste.  Here you will drive to the end of the road and then hang a left on HWY 180 (libre).  You are almost there.  Stay right at the fork in the road and follow the signs that will take you right into the park.  You must pay for parking.  If you were an early riser, the time should be about 8:30 am.  You have about 2-3 hours before the bulk of the HERDS start arriving, so get inside.  Once inside, you will be approached by some men soliciting to be your tour guide.  This is great because you probably don't know too much about this archaelogical site and these men are chock full of info.  The down side of this is that the museum forces them to charge a nominal fee of 500 pesos (yikes!) to do this.  As a strategy, politely tell each man that comes up to you that you are only here for a couple of hours and cannot afford 500 pesos.  Once you get inside and pay the entrance fee (100 pesos each) and begin to walk away from the main building you will probably begin to hear some "PPSSSSTTTTSS".  The tour guides will come up to you once again after your inside and try to secretly negotiate a better rate for their services.  Know this, the tour guides make the bulk of their money off of the large cattle bus groups.  You have arrived here WAY BEFORE THEM.  Use this to your advantage.  Tell them that you only want like a 2 hour tour so that way they will be able to finish with you and go negotiate another tour once those buses of people start coming in.  You should be able to talk him into 2 hours for 200 pesos.  Getting a tour guide here is highly recommended unless you are a Mayan expert yourself.  They have SO MUCH information that will astound you.

You should start getting hungry for lunch at about 11am.  You could literally spend ALL DAY at Chichen Itza but won't want too once you start seeing it get crowded.  Once done, get back on the road you were just on heading east (HWY 180).  Avoid all signs that say "Cancun Cuota".  This will take you back to the toll road.  Make sure you are on the "libre" road.  A great lunch awaits you in Valladolid.  HWY 180 will take you right into the "zocalo" of this colonial town 45 min. from Chichen Itza.   About 3-4 blocks east of the Zocalo is "Cenote Zaci", which pretty much amounts to their local swimming hole.  There is secure parking here and a very excellent restaurant that take very good care of foregin visitiors and have great authentic Mayan cuisine.  Please try the Cochinita pibil, pollo pibil, and poc-chuc.

Ask your waiter for proper directions to get back on HWY 180 (in case you are confused even though it is only about 2 blocks over) and continue heading east towards Chemax.  Again, make sure to avoid all signs that say "Cancun Cuota".  Stay on "libre".  You will not enter the town of Chemax and instead drive around it on a detour road.  After passing Chemax, your next stop is Coba.  You will come to a rotunda there.  One exit will take you back to the "Cuota" road (again), the other to Tulum, and the one to your right will take you into the ruins of Coba.  The time should be about 2pm once you get there.  Head right towards the ruins.  You will pass a lake on your right, and the ruins will be on your left.

Entrance to Coba is a little less expensive than Chichen Itza.  You can get a guide here if you wish, but  your 100 pesos may be better spent on a  "pedi-cab" that will take you along the trails of the site.  The site is huge, so trying to do it on foot could take you upwards of 2-3 hours.  Instead, choose to investigate the front of the site on foot, by yourself, and then hire the pedi-cab to take you to the pyramid (which is really the centerpiece here).  You are allowed to climb this pyramid.  Don't be afraid, just do it, and you will be rewarded with a spectacular view of the Yucatan jungle.  Once done with the pyramid, the pedi-cab will take you back to the entrance.

Follow the road back to the rotunda (ask the parking lot attendant for help if necessary).  You will now take the exit for Tulum and back to HWY 307.  About 6-7 km before you get to Tulum, you will pass the Grand Cenote on the left.  The time should be about 3:30-4pm.  For another 100 pesos this makes for a GREAT WAY to refresh yourself after visiting two ruins.  Once done, head back out on the road towards HWY 307.  You will get to this highway at Tulum.  Hang a left, and head back north towards PDC.  Depending on how late it is, you may or may not want to stop for dinner along the way or simply wait to get back to your hotel.