In Opal City.
After entering the city, Link found a dark corner to change into another attire. He took off the Flame Controller Magician's robe and the ice bear cloak and changed into a very plain-looking gray long robe. He then used a non-toxic alchemy potion to dye his hair brown, then tied a plain cloth around his head. Added to his already unremarkable looks, Link had now transformed from a Master Magician into a plain pedestrian.
Once that was done, Link began to snoop around the city for any news of unusual events that recently occurred. He'd spent a hundred gold coins within half an hour doing this, after which his understanding of the underworld in Opal City had deepened. He'd also gathered much information about Celine's current plight.
