Plato is a 61 mile wide lava filled crater sitting on the northeast ‘shore’ of Mare Imbrium. Estimated to be 3.8 billion years old, the crater is only slightly younger than the mare. And while the crater is prominent in this image it was not the focus of the photo. Running NE from the crater (diagonally down to the left) is a sinuous rille.
Crater Plato (mouse over for labels.)
In fact, there are three different rilles that are collectively known as Rimae Plato (two are shown here). Based on the current formation theory, the long depressions are the remains of collapsed lava tubes. The low lighting angle accentuates the depth of the rilles making them much easier to see.
This image is the sharpest 10% of 3113 frames taken at 25 fps. Each frame is exposed at 1.1 ms.