Memoria is ancient Greek stylish, not so big city. It consists ancient Greek styled buildings with ancient Greek written to them and statues, most noted one amongst them is a statue dedicated to Mnemosyne, the goddess of memory whom statue is located in the middle of the Forum.
First time Memoria appears in Episode 21 when the Guard searched kidnapped children. They found them but a little too late for everyone. Later in Episode 22 they found children's kidnapper Mary-Anne from her chambers and after a fight, managed to capture her.
Erika returns to Memoria in Episode 23 when she felt mysterious pull towards the place. She had used fire magic in Episode 22 and wanted to know more about herself and her possible powers. She returns home in Episode 24 but is again forced to go back in Episode 25.