There's a pretty continuous line between the carolus guilder and the euro. For example, the modern-day (2002) guilder was fixed at an exchange rate of 2.2 GLD = 1 EUR. Previous coins also had a more-or-less fixed ratio, aided by the value of the gold and/or silver they were made out of.
If you want to treat it like a completely separate coin, you'd have to buy historical carolus guilders in auctions. They seem to be worth about €1500 [0], although the same amount of gold can be bought for only €240.
If you want to treat it like a completely separate coin, you'd have to buy historical carolus guilders in auctions. They seem to be worth about €1500 [0], although the same amount of gold can be bought for only €240.
[0]: https://www.ma-shops.nl/henzen/item.php?id=77815