Moon colonization – many lava tube caves, water and high amounts of titanium:
"The moon has many hundreds of large lava tube caves. The Lunar Reconnaissance
Orbiter has now imaged over 200 pits that show the signature of being skylights
into subsurface voids or caverns, ranging in diameter from about 16 feet (5
meters) to more than 2,950 feet (900 meters), although some of these are likely to
be post-flow features rather than volcanic skylights."
See:
https://www.nextbigfuture.com/2017/1...-titanium.html