They say to "write what you know." I confess to not completely understanding this advice. I certainly set a lot of stories in physical environments that I'm familiar with. Most of the cities/towns in my tales are based either on New Orleans or on my small home town of Charleston, Arkansas. Many of the characters in my stories have similarities to myself or to other folks I know. When I have characters use guns, or ride motorcyles, or drive cars, I usually select ones that I've fired, or ridden, or driven. But can't I have a character who flies a plane? I never have, and believe me you wouldn't want me flying yours. Or what if I want to set a tale in the Sahara desert, or on the moon? I've never been to either. What if...I want to write a story with a main character who is a woman? I don't think I've ever been one.
Many of my favorite stories by other writers are set on worlds that neither the author nor any other human has ever visited. Many are set on worlds or in places that have never even existed, and never could exist. Thank the muse that those writers didn't stick with "what they knew."
"Write what you know" has to be expanded. Use what you know, certainly. Use it as the basis, the core of your story. You know emotions, needs, wants. You know sickness and health. You know dreams. But don't let not knowing stop you. Write what you can know, what you can learn. Most of all, write what you can imagine.