Scientists have discovered a "front door" to a massive cave on the moon, which could provide a pristine record of lunar volcanism. The cave is located beneath a collapsed pit in the Sea of Tranquility and was found using orbital synthetic aperture radar (SAR) instruments. Researchers believe that studying the rocks within the cave could give insight into the history of volcanism on the Moon.
Source: https://www.livescience.com/space/the-moon/lunar-lava-tube-revealed-beneath-collapsed-pit