the-witcher-3
I've collected a bit of foreign coins, which merchants unfortunately don't accept as payment. The descriptions of these in the inventory helpfully states that I can exchange them for crowns at the Vivaldi bank in Novigrad.
I've been to Novigrad now, but it's really, really large and I didn't see the bank so far. Where exactly is this Vivaldi bank in Novigrad?
Complete the quest: "Ladies of the Wood".
I finally found the Baron's wife, it turns out the part about investigating all remaining leads refers to the leads about Ciri. There are two quest series about Ciri in Velen, and at this point you have to follow the other quest series to complete the "Family Matters" quest, and "Ladies of the Wood".
Enter the city from glory gate take the left on the main road and circle around the "block". Before the intersection you should see a door (as in the picture) on the right, knock and you're in "putrid grove"!
Below image of the Door, and an image of the map facing the door.
Best Answer
According to this article.
This article has a picture of where the bank is located: