Fra Mauro is the worn remnant of a walled lunar plain.

The outer door popped silently and swung inward-and I looked out over the bleak bright surface of a lunar plain.

Bordering the northern rim is a large, unnamed lunar plain.

The big lunar plains are called maria or seas.

A quick trip to the Moon provides the answer: Imagine yourself standing on a dusty lunar plain looking up at the sky.

He was standing on the lunar plain and looking at the stars, which were just as distant as they were back on Earth.

Dar frowned, and his gaze drifted away, out toward the stark, cruel sharpness of the lunar plain.

Tom had lined up on a huge crater near the lunar plain called the Mare Im-brium.

Over the wild, lifeless lunar plains and mountains he flew at high speed, through the blazing sunlight.

Crane had a brief vision of the sea floor- stretching away in all directions like a grayish lunar plain.