other colonial cities in Latin America

[Sue100]

As much as I love GTO, I feel as if I am shortchanging myself by only coming here and never going anywhere else. Usually I come for a couple of months. What I treasure about GTO:
the weather (especially that it does not get hot and humid)
the walkability
the colonial beauty
the low proportion of expats to locals
(related to the above point) the fact that I am forced to use my Spanish because few locals speak English.

Has anyone spent time in other colonial cities-- in Mexico or other countries in Central or South America-- that meet these criteria? I would be grateful if you could share your experiences and make some comparisons.