How can Castillo de San Marcos be used as a primary source to identify St. Augustine's significance? Objective Students will analyze primary and secondary sources to identify the significance of St. Augustine by virtually exploring the Castillo and answering the discussion questions. Background Review the Virtual Field Trip before assigning to students. Please plan on downloading the virtual field trip before sharing with the students. The "Download" function appears in the upper left corner once you open the link. This reduces the lag time and create a more user-friendly experience. Preparati Duration: 90 Minutes.