Mare Humorum is also known as the Sea of Moisture. It is a rather small circular impact feature located on the visible side of the Lunar landscape. It measures approximately 825 kilometers in diameter and was formed an estimated 3.9 billion years ago. The floor of the mare was flooded with lava which extends beyond the basin rim is several places. This lava floor is estimated to be in excess of 3 kilometers in thickness. The large crater located on the upper left edge of the mare is Gassendi. This crater was considered as a possible landing site for the Apollo 17 mission but was rejected in favor of the Taurus-Littrow Valley.
An image with the larger craters surrounding the mare identified can be viewed here.