If you are cruising the Mexican Rivera or doing a Panama Canal cruise, one of the stops you will most likely go to is Acapulco.  Most of the people on your ship will be aiming to see the famous cliff-divers.  This means if you simply cross the road from where you ship docks (or did on our cruise) you can have the fabulous Museo Fuerte de San Diego (Fort of San Diego) almost entirely to yourself to explore.

The fort was originally built in 1616, and rebuilt following a massive earthquake in 1776.   There are a number of exhibitions rooms which depict the history of Acapulco and the fort itself.

I found the hours and openning days listed on one website but I couldn’t find an official website in English.  I found another site that said it was $48.00 pesos for entry.

The Museum is open to the public Tuesday through Sunday from 9:30 AM until 6:30 PM. 
Tuesday through Saturday admission is $30.00 pesos per person.
Sundays admission is free. 

If we assume entry fee is $50.00 pesos, thats less than $NZ5 or $US4, so pretty cheap.  I don’t recall if we paid in US$ which was most likely or if we used our credit cards.  We certainly didn’t have any Mexican Pesos.