@fenix is your hub for everything you need to craft, including mats, crystals, and an Auction House, plus a great hangout spot. All shop prices are 1 gil, and each NPC has almost everything you need to level a craft! See below for a map and the items for sale.
Receiving Synthesis Support
Trade a Terra Crystal (which can be purchased from the Crystal NPC) to the craft's NPC of your choice, and you will receive synthesis support for that craft!
The crystal will be returned to you.
NPC Functions & Locations
The red icon in the middle of the map shown below is where you are placed when you use the @fenix command. Each marker represents an NPC. The NPCs have an appearance that relate to the craft they represent, and they sell basically every ingredient you'd need to level a craft to 100. The AH looks like Maat!
Middle of east wall. Sells all types of crystal clusters, and also High Quality crystals.
Middle of west wall. The NPC looks like Maat getting ready to punch you!
Just east of the northwest corner.
Middle of the north side.
Near northeast corner.
Near southeast corner.
Middle of the south side.
Just east of the southwest corner.