The Loreta is an architectonic treasure of Kosmonosy and is known even far abroad. It was built upon a request of Jakub Heřman Černín of Chudenice by the Italian architect Giovanni B. Alliprandi at the site of the original parish church of St. Martin destroyed during the Hussite Wars. The Loreta consists of a rectangular central building of the Santa Casa. It is a copy of the first building of this type in the Italian town of Loreto, which allegedly concealed the house where the Virgin Mary had lived and which was transported to Loreto in the 13th century.

The walls of the Santa Casa are decorated with reliefs depicting scenes from the life of the Virgin Mary and statues of prophets in niches. The interior is decorated with imitations of original frescos in Loreto, Italy. The Santa Casa is surrounded by ambits opening into yards through a row of semicircular arcades.

The eastern side features the Baroque chapel of St. Martin, which has an oval shape and a Byzantine cupola. Under the chapel, there is a crypt where thematic exhibitions regularly take place. North of the Loreta, there is a four-level slightly slanting belfry from 1673.