The Garamsythe Waterway
There's a save crystal here, save an heal up here if you like. Climb the stairs and follow the path - this section is relatively straightforward, so just head north and right on your map. Continue east, you'll reach a sort of shallow-water area, keep your eyes peeled for chests and what have you - you can level up and gain a few bits of loot from the rats and other monsters that hang around here.
Cross the bridge and up the stairs, one path leads to a dead end which may have a chest that has a high enough chance of containing a Mage Masher, it's entirely up to chance.
Head up to the northwest corner of the screen, enter the Royal Palace of Rabanastre.
The Royal Palace of Rabanastre
Grab the map from the urn, save your game at the save crystal and go through the door. Don't touch the two chests to your right (in the south-west corner) unless you don't want to get the Zodiac Spear.