Literally translating as "witches cauldron", the German compound noun Hexenkessel means something along the lines of "pandemonium". Contrary to the English word, it always refers to a location - one that is characterized by loud uproar, disorder or chaos.
The most important component of the word's meaning however is stirred up (no pun intended) by the image of a witches cauldron: The Hexenkessel is most of all characterized by utter distress of whoever is thrown into it. Imagine a pedestrian unwittingly running into a violent demonstration, or somebody who grew up in the country visiting a big city for the first time.
Collins dictionary adds the note "(no art)" which, while perhaps not universally true, gives a sense of where the figurative meaning applies and where not. Today the word is most frequently used in the context of sports - if a team has an away match, the fans of the rival team typically turn the stadium into a Hexenkessel for the guests.