Teens are exploring a cave and find a space ship.
I think Star Dancer by Sir Winston.
Long since deleted from SOL. He has self published several books in this series, but I don't know if he has finished the series.
Teens are exploring a cave and find a space ship.
https://storiesonline.net/series/580/the-new-federation
The series starts with the teens doing some caving and they fall, one breaks his back and the AI in the space ship saves them and heals him.