The church's crypt is a highly evocative place, which can be reached by going down to the area under the vestibule, between the two 20th century staircases. It is punctuated by 24 plastered pillars, engraved with plaques that commemorate the fallen of the First and Second World Wars. In addition, there are five wooden poles on which some of the Martyrs of Belfiore were hung, and a box that contain their remains. Although criticism is often made of the inconsistency between the upper and lower parts of the church, there can be no doubt whatsoever that the crypt was an integral part of Alberti's initial plan. In fact, the entire complex is based on the relationship between the lower and upper part, with the latter made possible thanks to the most secret place at the base of it.