Decision time: leave after lunch for a sound and light show at another Mayan ruins of Uxmal and Kabah returning at 10 pm or take the all day highly recommended swim in 3 of the local 'cenotes' (sen-o-tays). These are fresh-water swimming holes connected by spectacular limestone caverns and deep underwater rivers once sacred to the ancient Maya, covering the entire Yucatan peninsula.
 
I have never seen a light and sound show so this option was really tempting. Pity we can’t do both!
 
Anyway in the end Raul the local guide took us to go swimming in the 3 cenotes or what I know them as sinkholes won. Both were about the same 450 pesos / NZ $ 42 / US $ 34.
 
Lunch was at a local hacienda restaurant El Dzapakal. Poc Chuc or a pork loin marinated in sour orange juice served with refried beans, tomatoes, avocado, roasted red onion for 75 pesos / NZ $ 7 / US $ 5.70. That plus a Negro Modelo at 27 pesos / NZ $ 2.50 / US $ 2.10.
 
A cenote from Yucatec Maya "well") is a natural pit, or sinkhole resulting from the collapse of limestone bedrock that exposesgroundwater underneath. Especially associated with theYucatán Peninsula of Mexico, cenotes were sometimes used by the ancient Maya for sacrificial offerings. The term derives from a word used by the low-land Yucatec Maya, "Ts'onot" to refer to any location with accessible groundwater. Cenotes are common geological forms in low latitude regions, particularly on islands, coastlines, and platforms with young post-Paleozoic limestones that have little soil development.

Cenotes are surface connections to subterranean water bodies. While the best-known cenotes are large open water pools measuring tens of meters in diameter, such as those at Chichén Itzá, the greatest number of cenotes are smaller sheltered sites and do not necessarily have any surface exposed water. The term cenote has also been used to describe similar karst features in other countries such as Cuba and Australia, in addition to the more generic term of sinkholes.

Cenote water is often very clear, as the water comes from rain water filtering slowly through the ground, and therefore contains very little suspended particulate matter. The groundwater flow rate within a cenote may be very slow. In many cases, cenotes are areas where sections of cave roof have collapsed revealing an underlying cave system, and the water flow rates may be much faster: up to 10 kilometers / 6 mi) per day. Cenotes around the world attract cave divers who have documented extensive flooded cave systems through them, some of which have been explored for lengths of 100 km / 62 mi or more. Thanks Mr Wikipedia.

The horse drawn like jiggers taking 4 of us along the 200 year old 9 kilometres track to the 3 holes.

Was the best left to last?

Actually I enjoyed the second one. Suppose it was the narrow hole at the top. Learnt my lesson in Indonesia when swimming in the fresh water Green Canyon this time took up the offer of a life buoyancy vest so that I could just float and admire the view above from below.
  
We got back late - close to 5 pm so my “hop on hop off” 90 min tour of town was not really possible as I wanted a shower first.

That evening it was pizza on the hotel roof. There is effectively no dusk. Just suddenly it is pitch black. The moon was just rising. No stars. Jet black skies above and the lit cathedral was not too far away. A gentle evening breeze kept things nice at 23 C.