My characters are all about level 41 atm and I found a way that they can level up in quite a short space of time. First teleport to the Stilshrine of Miriam. Enter the Stilshrine and immediatly turn left and go down to stairs on the left-handside wall. These stairs should take you to a place called "Cold distance" from here go straight forward until there is path on the right-handside, take this path and you'll be taken to a room called "Walk of Prescience" turn right and walk until you hit the wall then turn left and follow the path, killing the balloons when you reach them. Turn left at the end of this path and defeat the enemies here. Go down the stairs and you should enter the "walk of reason" This is the place to train. Cast haste on all of your party members and get ready for quick levelling. The undead enemies you will encounter here give about 300 exp each (double that using embroided tippets) and if you are above level 30 they should die in no more than two or three hits. Work through this room killing the undead enemies until you reach a doorway, open this and enter the second part of the "walk of reason" be careful of the trap in the centre of the room and dispatch of the undead enemies. Once the room is cleared open the next door to the biggest room in the Stilshrine of Miriam. There are loads more undead enemies here. Stick to the lower level pathways of the room to face many undead enemies. This is also a very good way to get a massive chain level and therefore get lots of loot. Once the enemies are gone return to "Cold distance" making sure not to kill enemies that ar enot undead (you will ruin your chain) once in cold distance return to "Walk of reason" and repeat the process.

I have used this method a few times and it works wonders. This morning I grew about 2 or 3 levels for each character and got enough loot that sold for about 100,000 gil in probably just a little over an hour.