- with low-cost transport, where would international astronauts go? -

Rilles (rhymes with "thrills") appear to be lava tubes that have collapsed. This results in a long, narrow trench that can extend for as much as hundreds of kilometers. Beyond where the rilles start and end, there might be pristine caves that could be broken into.

Prinz: Multiple rilles in the same area running in different directions. Each was a formed around the same time as the others. There was a plan to send an Apollo misson to this area but in the end, this mission didn't happen.

Sharp: This is the longest rille on the Moon. 500 km? long? Seeing only part of it (widest part). Close to where the Chinese Chang-e 5 will be going.

Hadley: Was visited by Apollo 15. Landed close to it and they drove right up to the edge. It is the only one that has been seen close up. It was chosen because it was within reach of the Apollo vehicles (near the equator) and it was also close to the mountains.

Next: Valleys