The German noun das Unglück is often translated as "misfortune" or "bad luck" in English:
But das Unglück can also be an accident or a disaster:
Es war ein großes Unglück mit dem Vulkanausbruch in Island.
It has been a big disaster with the volcano erupting in Iceland.
Caption 3, Reisen: während des Vulkanausbruchs
There is also an idiomatic usage of das Unglück:
Wir haben Glück im Unglück, dass wir jetzt ein paar Tage länger hier in Spanien sein dürfen.
We have luck in misfortune that we may now spend a few more days in Spain.
Caption 24, Reisen: während des Vulkanausbruchs
The rendering as "luck in misfortune" is literal, but the idiom is akin to the English "a blessing in disguise," when good things come out of seemingly bad occurrences.
But let's not end this lesson on a sour note, instead let's give it das Happy End or das Happyend (a German pseudo-anglicism for a "happy ending"). The opposite of das Unglück is das Glück, which can be translated as "happiness," "good luck," or "good fortune," among other happier words. Do a search for the word Glück on Yabla German and see how the different contexts of its usage can help you understand it better in a real world context.