Final answer:
The unfinished castle is in Spain, while Portugal began Atlantic exploration and Spain was the first to establish colonies in the Americas.
Step-by-step explanation:
The castle that was abandoned before construction finished is located in Spain. It is widely known as Castillo de Colomares, a monument dedicated to the life and adventures of Christopher Columbus. As for the questions about Atlantic exploration and colonization, Portugal initiated the era of Atlantic exploration, while Spain established the first colonies in the Americas. These historical feats were driven by the countries' pursuits for new trade routes and the desire to expand their empires.