Starting in the present day and travelling right back in time to the extinction of the dinosaurs (the meteorite that wiped out the dinasaurs hit north of Merida), the Gran Museo del Mundo Maya is a fantastic introduction to all things Mayan and a fascinating place to spend an hour or two.
The building itself is well worth a visit (and not just for the air conditioning, although you'll welcome this on a hot day in Merida). A great place to go for an intro into the Mayan world before visiting the ruins for real.
There is a cinema in the building that occasionally screens movies and opera - check out their facebook page for details.
Mon-Su: 08:00-17:00