DND horizon help please!

Hey all- I'm running a custom DND campaign based on horizon zero dawn. I'm winding up to where my players encounter a cauldron. Can some of you share what encounters in a cauldron that made you say "whoa" or perhaps even your own ideas for what would be neat to encounter in a cauldron?

Edit: getting some great ideas so far, hoping to print out some modular rooms with each of your ideas. Now to find or make files and start watching playthroughs to refresh myself on terrain and things in cauldrons