Return to your airship–you do remember where you parked it, right (the pier north of Ancheim)? After taking off, set a course for the landmass north-west of Ancheim, where the next orange exclamation mark lies. In the centre, there’s a lake where you can park the Eschalot and a wooden pier to get back to land.
A detour every now and then never hurts… unless there are vicious monsters abound. Hmm, wait a second…
From the pier; it’s just a moment’s walk to reach the old man’s residence, across the wooden bridge. According to the old Sage Yulyana, the vestal garb can be repaired with rainbow thread from the nearby Vestment Cave. Sounds like another healthy adventure then! The next day, the party will be ready to set off in search of the thread.
Before you go; be sure to snoop around the bottom-right corner of Yulyana’s residence, where the Adventurer and his (talking!) animal companion are selling items. Some of the stuff here is pricey, so don’t overspend! Inspect the room in the top-left corner to find a Peace Ring and check the area right of the bridge for an Antarctic Wind (combat item).