Alliterations? What is a noun that starts with the prefix un?

I have an alliteration that i have to do, the word is unearth .. you can change it like.. unearthly... so on. So far I have underneath the underground railway in the United States was an unearthly.......... i need a noun. Thanks! The one thats fastest and makes the most sense gets best answer! If you try to write a new alliteration... good for you, but It doesn't help... no best answers... maybe even a thumbs down. Thanks :D