San Juan - Fort San Cristobal Look Out - A Beautiful Close Up View Of An Observation Window In A Guerite, Or Sentry Box, With Another Guerite And The Caribbean Sea In The Distance Along The Coastal Side Of Fort San Cristobal In Old San Juan, Puerto Rico. Also Known As Castillo De San Cristóbal, It Was The Largest Fort Ever Built By The Spanish In The New World, Designed To Help Protect San Juan From Land Based Attacks. Photo