Castles, often built on hills with extremely steep slopes, or on sea cliffs overlooking stretches of water, were difficult to conquer. Construction techniques and geomorphology of the area were a key factor in making castles impregnable to sieges of military troops or bands of pirates or robbers. Today, the same characteristics make them difficult to survey. In fact, there are huge difficulties in surveying fortified structures on the top of hills or on the edge of a precipice. Such geomorphological features sometimes make the survey difficult, time consuming and expensive and unsafe for operators. Today, these problems can be reduced through the use of drones and photogrammetric processing tools which are based on Structure from Motion algorythms and are easy to use. This method allows us to acquire data with geometric resolution in order to map and study masonry characteristics, as well as analyze and monitor decay and crack patterns for restoration purposes. In this paper, we will discuss the potential of drones and modern photogrammetry techniques in architectural surveys and applied to three case studies. These include the castle of Isabella Morra in Valsinni (Basilicata, South Italy), perched on a cliff; the medieval citadel of Uggiano in Ferrandina (Basilicata, South Italy) in an advanced state of degradation and on a plateau with high geological risk; and the San Fernando Fuerte to Bocochita (Cartagena de Indias, Colombia) overlooking the sea.