https://www.chrono.gg/How does it work? It is a mystery
Enter a Steam key and you'll receive one of the other Steam keys people "threw away" when Chrono did this last year. They might be good, they might be bad. They're probably really, really bad. There's even a chance they might not actually be valid, but you were never really going to play Bad Hotel, right?
You can only do this once, and the key disappears if you reload the page. Time to sift through your Humble library.
I got There's Poop In My Soup.
Edit: You technically don't have to put a real Steam key in for the Hole to give you something in return, but would you purposely bring that karma upon yourself?