This fountain, know as the Fontana del Mascherone di Santa Sabina,
is in a small courtyard just off the main side entrance of Sta. Sabina.
Designed by Giacomo della Porta it dates from ca 1593.
The "mask design" is also seen in a few other fountains in Rome, with the face of a man overlaying a shell background.
The fountain is about the size of an oversized bathtub, and the water drips from the mask-like face.