Merida is a trip into historic Mexico and it’s beautiful architecture. The old section is a glimpse of colonial Mexico. It is also one of the safest cities in Mexico. On Sunday nights there is salsa dancing in the streets.
If you are doing a luxury week at Vidanta Riviera Maya in the Grand Luxxe it is too far for a day trip. You should add 2 or 3 days onto the beginning or the end of your trip.