The inner wall of Grimaldi has been so heavily worn and eroded by subsequent impacts that it forms a low, irregular ring of hills, ridges and peaks, rather than a typical crater rim.

The mare lava floor is the most notable feature of this crater, forming a flat, relatively smooth and featureless surface with a particularly low albedo.

To the northwest, rilles belonging to the Rimae Riccioli approach the western edge of Grimaldi's rim.

Grimaldi has a history of transient lunar phenomena, including occasional flashes of light, color patches, and areas of hazy visibility.

By convention these features are identified on lunar maps by placing the letter on the side of the crater midpoint that is closest to Grimaldi.