Diameter 90 km | Eponym Lake of Happiness | |
 | ||
Lacus Felicitatis (latin for "Lake of Happiness") is a small patch of the lunar surface that has been inundated by flows of lava, leaving a level patch with a lower albedo than the surrounding ground. It is located in Terra Nivium, an area of continental ground to the north of the Mare Vaporum. About 70–80 km to the northeast of this area are the Montes Haemus, along the southwestern edge of the Mare Serenitatis.
The selenographic coordinates of the Lacus Felicitatis are 19.0° N, 5.0° E, and it has a maximum extent of 90 km. In outline it has a bent shape, with a wing to the northwest and another to the east. The border is somewhat uneven, and it is surrounded by rugged lunar surface.
Three tiny craters within this formation have been assigned names by the IAU. These are listed below.
Ina is a semi-circular depression that is only about 30 m deep and is difficult to image from the Earth.
In November 2006, it was suggested that Ina was the result of a gas eruption in the last 10 million years.