Ghosts of Mars, etc.

http://www.theofficialjohncarpenter.com/pages/themovies/gm/gm.html
Movies can provide for some interesting speculation as to what use to be on an ancient world.
http://en.wikipedia.org/wiki/Ghosts_of_Mars
If a planet has suffered some kind of a global catastrophe, some remnants might remain upon the surface.
http://www.paranormalghostsociety.org/cydonia.htm, http://www.tarrdaniel.com/documents/Ufology/cydonia.html
Some peculiar things might also be found on what use to be a seabed.
http://www.enterprisemission.com/excuses.htm,
http://www.youtube.com/watch?v=oC31pqk9sak
Then even more things might be found deep underground.
http://www.wired.com/wiredscience/2010/01/mars-earth-close-encounter

http://mars-earth.com/cydonia_eygpt
Did some ancient technology make if from Mars to earth?
http://www.youtube.com/watch?v=sxllptqVSYk&feature=related
Its mighty peculiar how some shapes seem indicative of ancient technology.

http://www.wired.com/wiredscience/2010/01/gallery-mars
Could Mars have looked more like the earth about a billion years ago?
http://www.theatlantic.com/technology/archive/2013/01/a-martian-dream-heres-what-the-red-planet-would-look-like-with-earth-like-oceans-and-life/266791