Invisible Serdica is a free application that gives you the opportunity to explore the hidden and most attractive historical and architectural treasures of Sofia, the capital of Bulgaria, by providing images, videos, 3D models and interesting stories and legends about the locations, different from the standard information you will find in any tourists guide. As a start-up 5 key places were chosen: 1/ St. Sofia Church2/ St. George Rotunda Church3/ The Amphitheatre of Serdica4/ The Largo (incl. the places around and also hidden beneath)5/ The tombs hidden below the square of the National Assembly and around itMost of the content included in the application is taken from old books, which contain unique information, gravures, images and drawings. The idea is to make this interesting but not well-known data available for the wider public and thus make the most inspiring places in Sofia (its former Thracian and Roman name being Serdica) even more attractive. Another, also important aim of the application is to promote NALIS catalogue by providing links to books and other published works (that are related to the places chosen) included into the catalogue.Invisible Serdica application can be useful not only for the users of NALISs web site and catalogue and bibliophiles, but also for tourists and visitors of Sofia, as well as for students and teachers and serve educational purposes.- , - , , , , 3D , , . 5 :1/ . 2/ . 3/ 4/ (. )5/ - , , , . - , - ( ) -., , , . , , , .