If you embark on an activity that people haven’t experienced before, you’re entering uncharted waters or uncharted territory.
“Uncharted” comes from the word chart meaning map, like the French carte. A thing that is uncharted is something that’s not on the map, or that’s unknown or unfamiliar.
The term is often incorrectly written as unchartered, which would mean “not having a charter or written constitution”. The word is rarely used, other than as an incorrect version of uncharted.
You can read about the difference between uncharted and unchartered and a whole lot more, in the Clifford & Co editorial style guide.