Here can be seen the famous icon of Santissimi Salvatore Acheiropoieton ("not made by human hands") which on certain occasions used to be carried through Rome in procession. In the Holy Year 2000 the pope ordered it brought to the Vatican for a celebration. Now Ukrainian and Russian pilgrims often pray here. Sadly, an entrance fee is now charged to enter this holy place.
Read about it here at the bottom of this link: