First underground secret base in literature?

A friend and I were recently discussing the iconic secret underground base trope and it’s history in fiction. It got us wondering what the first recorded mention of a secret underground base was?

The earliest mention we could think of off the top of our heads was Zorro which was first published in 1919. Google wasn’t much help with trying to find anything earlier, so we thought why not ask the literature subreddit as there’s bound to be some people on here that have read earlier works with that trope

We’d like to try and track the history and evolution of the trope in literature, so if you know of a work prior to 1919 that mentions or references a secret underground base, either directly underground, in a cave, or in a cliff, please let us know the name and release year so we can take a look

Thank you in advance for any replies