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

Irregular mare patches (IMPs) are some of the most visually interesting phenomenon on the Moon. These are fresh, rough irregular surface that should make for some striking images while crew are exploring. It is thought that these patches are due to some form of volcanism with gaseous discharge. Here is a lunar map showing that the patches are located on the mare.

Sosigenes Graben: The following two lesser IMPs could be the first for astronauts to visit. Whereas not the largest, they could be the first visited and so of great interest.
Nubium: Imagine international astronauts walking in the valleys and climbing up on the plateaus, and examining and sampling the deposits. Much of the science to determine the cause of these formations would be figured out during their exploration.
Cauchy-5: The next two IMPs are not as large as Ina but should still be quite interesting to explore.
Maskelyne: This is another interesting formation with striking features.
Ina: This is the largest of the IMPs and so very interesting.

Next: Volcanoes