From now on you can freely leave and enter Rabanastre and besides you have now access to the Lowtown. There are also new services available:
Map seller in Southern Plaza
Chocobo rent stables by every exit from Rabanastre (500g)
Run to Sandsea and talk to Tomaj. He'll give you a reward for killing Rouge Tomato: 300 gil, 2x Potion, 1x Teleport Stone.
No go to Clan's Centurio HQ in the northern district (to enter you'll need to show your Clan Primer to a bangaa standing in front of the entrance) and talk to Montblanc in order to be counted as a member of the clan.
Now go south and leave through the South Gate. On your left side you'll see a giant, round Gate. Use them to get to Lowtown.
This Gate is the nearest to Old Dalan's Place. You'll just need to go around the corner [screen 1]. But before you do that it's better to "plunder" the neighborhood first. You'll find some potions and a few gil. The treasure chests appear most often in Dead ends and collapsed corridors (as you can see on [screen 2]).
After talking with Dalan leave Lowtown using the same way you got in. Now go to Giza Plain.