There are several currencies circulating throughout the world of the Witcher 3: Wild Hunt, but the merchants will only exchange their wares for Crowns. The other coins you collect on your travels will have to be exchanged for Crowns if you wish to have any use for them, and there is no better place to do that than in the reputable Vivaldi’s Bank Novigrad. To exchange your Orens and Florens, speak to Vivaldi and choose the I’d like to convert some currency option. Orens and Florins are worth more than Crowns, however, so be prepared to leave the bank with a heavier coin sack.
The bank itself is not marked on the map, but you can find it in the main market square, west of the Hierarch Square signpost. It is close to the bonfire that was used to burn witches when you arrived in Novigrad. There are two large coins hanging from its front.
If you’re strapped for cash, you can also take out a loan at Vivaldi’s, but only if you have repaid the one you took out previously. Vivaldi also plays Gwent, if you’re the card-playing type.