It's just wunderbar, or fantastic, that English has so many loanwords from all over the world! They can help us express a lot of different moods — in this case, delight and joy.
Wunderbar is a German word. Wunder means "wonder," and the suffix -bar essentially means -able. So something that is wunderbar is capable of causing wonder. The word has slipped into English usage, probably because it sounds so similar to wonderful, which has the same meaning. The word is good for adding a bit of enthusiasm or flair when reacting to good news or describing a great experience: "Our trip to Europe was absolutely wunderbar!"