Great grandparents were Spanish nationals:

I am an American citizen with 50% Spanish ancestry. My maternal great grandparents were all born in Spain but my Spanish grandparents were all born in the U.S. I have already lived in Spain for 3 months, am fluent in Castellano, and am going to move to Spain to live and work in the next few months.

Does someone like me qualify for Spanish citizenship based on my heritage?

If not, how long must I reside in Spain to apply for citizenship?

If granted Spanish citizenship, will I have to renounce my American citizenship?

What is the longest period of time for which a visa can last?

Mil gracias para todos tus aconsejos!