It also occurred to me that rapid, efficient tunneling would be very nice to have on Mars, or anywhere in the solar system really. Underground is the only place you can get protections from hard radiation, when your planet/moon doesn't have the beneft of a magnetosphere and atmosphere. Tunneling habitats seems a good way to go.

At the risk of sounding like a one-trick pony I recommend trains :P Space trains. Like in Galaxy Express 999 (https://en.wikipedia.org/wiki/Galaxy_Express_999)