Right then, I thought I would post this up as a couple of people who I have spoken to that have finished the game didn't know this, so here is a thread for those of you who have finished the FFXIII storyline and think you are done 
Once you have saved your game after watching the credits, reload this save and you will start in the room before the fight with Barthandlues III and Orphan. You can then leave Eden and go back to Gran Pulse. From this point onwards you get to do LOADS of CP farming, digging up chocobo treasures and completing those harder Cie'th marks that you hadn't done.
Also of note is the extra crystarium level you will now have unlocked. Whereas before Orphan it was only possible to reach stage 9, you can now reach stage 10, an immensely expensive stage supplying thousands of HP per role as well as hundreds of each stat.
I would say it would be best to only do some of the makrs after this point, and thigns like the Adamantoise can inflict over 10,000 damage in a single hit, so you WILL need this extra crystarium level in order to survive their opening attacks.
Hope this helps those of you who have finished the storyline and thought that was the end of the playability
(Also it is only possible to get the Role Master and Master Seal trophies/ acheivements this way)

Once you have saved your game after watching the credits, reload this save and you will start in the room before the fight with Barthandlues III and Orphan. You can then leave Eden and go back to Gran Pulse. From this point onwards you get to do LOADS of CP farming, digging up chocobo treasures and completing those harder Cie'th marks that you hadn't done.
Also of note is the extra crystarium level you will now have unlocked. Whereas before Orphan it was only possible to reach stage 9, you can now reach stage 10, an immensely expensive stage supplying thousands of HP per role as well as hundreds of each stat.
I would say it would be best to only do some of the makrs after this point, and thigns like the Adamantoise can inflict over 10,000 damage in a single hit, so you WILL need this extra crystarium level in order to survive their opening attacks.
Hope this helps those of you who have finished the storyline and thought that was the end of the playability

(Also it is only possible to get the Role Master and Master Seal trophies/ acheivements this way)