Depends what ruins you're talking about. Chichen Itza is the most popular and about 2 1/2 hours away from Cancun. If driving yourself, get their early to avoid the masses of tourist buses. There's also Tulum and Coba ruins, these could be done in a day trip together. Tulum is a little over 2 hour drive from Cancun and Coba is about 45 minutes from Tulum. Tulum is definately the most beautiful, located right next to the ocean. Coba is my favorite. It's not as tourisy and the ruins can still be climbed. You can walk to the ruins, rent a bike, or get a bicycle taxi. It's in the middle of the jungle, so expect lots of heat and bugs. I did both trips to Chichen Itza and Tulum/Coba as day trips but they were really long days.

you can do a day trip but start early. there are organized tours some very inexpensive, take some of the hassle away. you can also rent a car the local bus is not a great option as you will see more of the bus than the ruins

Watch out for palm trees that can occur in the middle of the road!

Tulum is very close...Chichen Itza is a day trip...and be prepared for a long drive on an expressway with no exits. Gas up first and and refuel before you return.

Chichen Itza is a one day trip with bus and about a bit more than 2hours from Cancun. It is touristy but a must see. Tulum is about 2hours just diffrent direction with but and it is nice because its at the coast. Coba is not even 1hour from Tulum and you can climb the main pyramid what is quite an adventure. You should not miss them as well! Do both!

Chichen Itza is about 2-2,5 hrs drive and Tulum about 4,everything depends what time you going.You can manage either of them in one day trip.Enjoy!

Tulum is a great trip that can be accomplished in a day.

Depending on the ruins you'll visit most of then are in a 2 hour radius from Cancun (if you are driving). I don't think you can do overnight trips since there are no places to stay in the ruins but visiting could take most of your day (so get there early!) since most ruins are kinda dispersed.

if u wanna see some not so tourtisty ruins go to Palenque!! they are a 12hr bus ride away tho (from Playa del Carmen - probably 14hrs from Cancun). however i took an overnite bus so i didnt lose any day time traveling. the ruins are outstanding, located in the mountains and jungle. theres 8 pyramids and u can climb them ALL (unlike the ruins closer to cancun which u can no longer climb, except for coba). if your gonna go see a pyramid, u gotta climb it! no sense just looking at it. therea also a river that runs through the ruin grounds, and if u follow the trail alongside it, it leads to an awesome waterfall. u can take another overmnite bus back to cancun without losing another day. or u can spend a nite in a hostel / hotel and go see Agua Azul the next day - a nearby waterfall. happy travels :)

I prefer tulum and coba, see it in its natural state

Rent an old VW Beetle and drive there in less than 3 hours. Go early to miss the mass-tourisme (insanly crowded...), on the way back stop at one of numerous ceynote dive spots! Great scuba and snorkling.

I caught the bus from Cancun to Chichen Itza, stayed overnight in a bungalow at the Mayaland Hotel, pricey, but beautiful grounds, great staff. Best of all they have their own entrance to the archeological site, so you can go to the sound and light show at night (bit average) and be at the gates at 8 am next morning to beat the other tourists. The heat will drive you indoors by midday, handy hint, take umbrella for sun protection, can stay out longer.

2 1/2 hour drive... Go for the night.. it's a great stay!