We have to say that Gran Canaria's cultural attractions aren't expensive even if you do have to pay the entrance fee. All the big ones are under five euros per person and free for the under-12s.
The Casa de Colón is free on the first weekend of the month, World Heritage Day (April 18), World Museum Day (May 18), Canarian Day (May 30), St John's Day (June 24) and on Spain's National Day (October 12).
The CAAM modern art gallery and associated San Antonio Abad gallery, both in Vegueta, are free on the first weekend of the month (most of the time), on Wednesdays from 18.00 to 21.00, and also on May 18 for International Museum Day
The Museo Canario in Vegueta is free on Monday and Wednesday afternoons between 17.00 and 20.00.
The Cueva Pintada in Galdar is free on the first weekend of the month, World Heritage Day (April 18), Canarian Day (May 30), International Archaeology day (June 29), and James The Apostle's Saint-day (July 25).
The Jardín Canario botanical garden in Tafira is always free.
Yes, us too. Free opening days in Gran Canaria depend on which government department runs a particular museum, and on which direction the wind was blowing when they had their AGM.
Double check the free days and opening hours for your museum of choice on its website.