You can access the Hubble area by going to the red pillar and placing your fragments in the southwestern pedestal. When you get there, you will see two castles on your map, as well as some place you can enter to the south. Ignore that and enter the first castle to find out it's the Ruckers Castle, a name that should be familiar if you already did the Providence Scenario. There's really nothing you can here, which includes items to grab, so check out the shops, talk to the NPCs and then leave when you've had your fill. Continue on over to the east, entering the town of Hubble.
One of the pots next to the inn will have 5 gold coins , while the chest in the equipment shop will have a Magic Shield (requires the Magic Key). There is a barrel and pot next to the item shop, so break them open to find a Magic Water . One of the cupboards on the first floor of the northeastern house contains a Pointy Hat , while you can get a Seed of Magic and Bow Tie from the drawers inside of the well. If you enter the northwestern building and check one of the bookshelves, you can fight a Hexicon. Entering the big building on the western side of town will prompt a guard to get up and block the door further inside, so you won't be able explore.
So, the only place left to go is via the north exit, to Hubble Castle. Say that you are the Envoy to be able to enter the castle. As you can see from your map, the castle is split into your areas, with each one corresponding to an element (wind, earth, water and fire). Start off by going to the southeastern one, which is the water tower. There are two chests in this first area, both requiring the Magic Key, which contain 310 gold coins and a Cloak of Evasion . Head upstairs and you'll find a chest that's locked and by talking to the NPC nearby, you will be given a clue on how to open it.
To open it, look at the four openings around the chest and how there's a statue by the western one. Start from the outside and go through the western opening and exit the eastern one, then move around to the northern side and go south through those two openings. If done right, you'll hear a click and can open the chest for some Sparkling Holy Water . Hand it over to the man when he asks for you, and he'll mention about coming to see him in the Fire Tower later for a reward. Head on over to the Wind Tower by going north to the Earth one and then west, where you'll find a chest on the first floor that contains a Seed of Magic .
At the top of the Wind Tower are the former king and his wife, the mother of the current king. Speak with the mother and agree to help her out with delivering a message to the Grand Conjuratorium. Return to the second floor and go south to reach the Fire Tower, heading down to the bottom floor to find two chests with 250 gold coins and a Seed of Strength . You may have seen a scene with the central tower lowering, so return to the main entrance of the castle and speak with the guard there, only to be escorted out.
Exit Hubble and go to the blockade to the southwest, showing the guard there the Queen Mother's Missive when prompted and travel to the Grand Conjuratorium to the east. Enter the main building and you'll see some stairs surrounded by water in the middle of the area. This is a puzzle that is the exact same as the one chest in the Water Tower back at Hubble, so start from the west opening and enter it from the outside, then exit through the eastern one and do the same with the north/south ones to make a bridge appear so you can get to the stairs.
There will be two chests right at the bottom of the stairs, containing a Magic Water and Seed of Magic . Exit via the southern door to come to some graveyard area, so break the pots here to find 6 gold coins and a Mini Medal (#64) . Exit to the outside courtyard via the stairs to the south and go back inside the Conjuratorium, heading upstairs this time. In the one room with the big cauldron, talk to the Wizard-in-Chief (the Wizz from now on) and show him the missive. Of course, he thanks you for this small deed and asks you for a favor of his own; he wants you to retrieve a Starshard from a nearby cave.