If you are doing a Western Caribbean Cruise you are likely to stop at Cozumel. If you are keen on a full day shore excursion and want to see some particularly spectacular Mayan ruins, then definitely go see Tulum. From memory its a full day excursion as its a good couple of hours each way by bus but was worth the journey and was simply spectacular.
Tulum is unusual in that it was a fortress on the coast while most of the ruins, or at least the ones I’ve seen, tend to be settlements or ceremonial locations. Tulum is certainly one of the most picturesque ruins I have been to. As its literally, right on the coast, if you like to swim, take your swimwear as you may have time for a quick dip. It was sweltering the day we went as an afternoon storm was approaching, but the thought of sitting in sticky swimwear for the bus ride back didn’t appeal to me.
Tulum was one of the last cities inhabited and built by the Mayas; it was at its height between the 13th and 15th centuries and managed to survive about 70 years after the Spanish began occupying Mexico.
We saw loads of huge iguanas throughout the ruins which were fun to photograph.