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.
www.eutharan.com.
Just a heads up the www.eutharan.com link is longer working, it takes you to a Chinese sex site that looks like a Vegas billboard with a lot of bright flashing banners.