Forum regular kodemunkey found this unusual feature using the ACT-REACT Quick Map tool and posted in in the forum’s “Interesting Terrain” thread. It is located in the volcanic Gruithuisen region on the Procellarum – Imbrium border at lat 34.52345 : long -43.43379 and is part of a much longer chain of collapsed pits from a potential lava tube. There is more information on the LRO site.
Part of the tube is still intact which makes it particular interesting as it could provide a natural shelter for a future manned mission. Lunar “caves” such as these could be earmarked for the establishment of a lunar base to take advantage of the naturally constructed protective shield from cosmic rays, meteorites and extreme temperatures.
It’s unusual for such a striking feature not to have a name. Kodemunkey suggested the region should be called “Mare Hysterium.” It’s definitely a great area to explore and full of surprises. Here’s the NAC image: M102443238RE.