[2] This feature lies just to the south of the elongated Mare Frigoris, being separated by a slender arm of rugged ground and linked at the eastern extreme.

To the south is the Lacus Somniorum, separated from this mare by the joined craters Plana and Mason, and a strip of uneven surface.

[4] Located prominently just to the east of the midpoint of this feature is the 40 km diameter impact crater Bürg.

[7] The western part of the Lacus Mortis contains an extensive system of criss-crossing rilles collectively designated Rimae Bürg, spanning a length of 140 km.

The eastern wall of this pit appears to have collapsed, leaving a ramp with a ~22° slope extending from the mare to the floor.