Another nice shrine with fresh paint, this one has a history that dates back over 800 years. This San Polo sotoportego is supposedly the place where Pope Alexander III slept when he arrived in Venice in 1177. He came to Venice in disguise, exiled from Rome and on the run from Emperor Frederick Barbarossa.
The Pope put a special blessing here for anyone who comes inside and prays before the shrine, according to the wooden plaque above the entrance.
There are several other legends about this pope-on-the-run. One is that he worked as a janitor for six months at the convent of La Carita before someone recognized him and helped restore him to power. He also spent the night on the portico of the church of San Salvador. Eventually, the Venetian Republic (a neutral party in the dispute) intervened and negotiated reconciliation between the two enemies, and the spot where they kissed and made up is marked with a stone on the floor of Basilica di San Marco (another floor detail to track down).
There's a little statue of the sleeping Pope inside the shrine at the bottom.
2012 Update: Check out Yvonne's recent visit to this shrine. So many mysteries!