Bullialdus, 61 km in diameter, has an interesting pattern of relatively small secondary craters surrounding it except on the bottom side where there is an unusual 'causeway'-like structure extending for quite a ways. Halfway to the upper left corner is a prominent lunar volcanic dome, Kies Pi, with a large summit crater. Several rille structures also visible as well as a number of old flooded craters with only rims more or less still visible.