Lacus Solitudinis (Latin sōlitūdinis, "Lake of Solitude") is a small lunar mare on the far side of the Moon.

It forms an arcing feature with the concave side oriented to the northwest.

The eastern edge is relatively continuous, while the west is more irregular and disrupted by small craters.

[1] To the northwest of the northern end is the small crater Bowditch, a lava-flooded feature although it does not appear directly connected to the Lacus Solitudinis.

At the western end of the mare, the eroded crater Titius lies to the northwest.