Lacus Somniorum (Latin somniōrum, "Lake of Dreams") is a basaltic plain located in the northeastern part of the Moon's near side.

This crater forms the western end of the southern border, which extends eastward to about longitude 41° before turning northwest.

A buried crater with a 200 km diameter was detected in this locale by NASA's GRAIL experiment, forming part of the north wall of the mare.

Finally the lake curves back to the south, joining a region of rough terrain along the northern border of the Mare Serenitatis.

These were named for the crater Daniell,[3] a small formation north of Posidonius that is encircled by the Lacus Somniorum.