The site for the cancelled Apollo 19.
http://www.lpi.usra.edu/resources/mapcatalog/LAC/lac59/
http://www.lpi.usra.edu/resources/lunar_orbiter/images/img/iv_102_h2.jpg
http://astrogeology.usgs.gov/lo-cgi-bin/frameListPage.pl?mission=4&frame=097
www.lunar-reclamation.org/papers/lavatubes_ccc.htm