This article presents two unpublished drawings coming from the Largest Talman Album, a voluminous collection of architectural designs belonging to the famous collector and antiquarian John Talman, conserved at the Ashmolean Museum in Oxford. The sheets are attibuted to Pellegrino Tibaldi on the grounds of an analysis of the graphic and stylistic characteristics of the designs and are related to the Sanctuary of Santa Maria del Fonte di Caravaggio. In the seventh decade of the 16th century, on the wishes of San Carlo Borromeo, this building was the object of a radical redefinition both architecturally and in terms of cult worship. The designs are analyzed in the context of Tibaldi's activity at the sanctuary and are compared with sheets already known regarding the reconstruction of the temple conserved at the Biblioteca Ambrosiana and with a comprehensive autograph report conserved in the sanctuary's archive. Of particular interest is the analysis of the ground-plan characteristics of the two projects and their meaning in relation to the specific cult characteristics of the dual pole of devotion comprising the 'Fonte miracoloso' and the so-called 'Sacro Speco', that is, the precise location of the Virgin's apparition. The drawings illustrated in the article, today conserved at Oxford, reveal the particular attention paid by Pellegrino Tibaldi to the design of the sacellum used to preserve these venerable testimonies. The purpose of the complex definition of the small building was to exalt the main pole of worship inside the vast sanctuary and to regulate access to the two distinct memorial sites by different types of pilgrim. Lastly, the history of the ownership of the drawings is investigated in an attempt to reconstruct the reasons for their entering the Talman collection.