Here is how the old tunnel was discovered and Vice Principal Luna shows her story in Fantasyland Rescue.
Just then, Yuna begins to notice about the old tunnel that was never used for many decades.
Princess Yuna: Hey, Guys, what's with this old tunnel?
Twilight Sparkle (Human): This old tunnel? That used to be for traveling to Equestria if it is possible, it's never been used for many decades.
Lightning McQueen: How great would it have been to see this place in its heyday!
Sunset Shimmer (Human): Oh, I can't tell you how many times we've dreamed of that. But one of these days, we'll find a way to get it back on the map.
Princess Yuna: Yeah. Hey, listen. Thanks, You guys, for the ride.
Dipper Pines: We had a great time. It's kinda nice to slow things down every once in a while.
Portal Glow: I second that.
Tillie: You're welcome.
Then, Tom, Blinky, and their friends came running to Yuna and her friends.
Splodge the Kangaroo: Hey, Yuna, listen! If anybody asks you guys, we were out looking at some animals, okay?
Princess Yuna: What?
As if to answer her question, a bunch of herbivore dinosaurs came stampeding towards Yuna and her friends and into town.
Princess Yuna: Whoa!
Portal Glow: Stampede!
Zephyr Breeze (Human): Run for it, Sis!
Fluttershy (Human): Oh my!
So, Fluttershy has to used the stare as the dinosaurs were brought together and were about to scatter not before the horn from the firetruck spooked them causing the dinosaurs to scatter about in town. As a triceratops and the gallimimus went into the super market they started eating some fruits and veggies in the produce section.
Portal Glow: There's a Gallimimus on the loose!
Princess Yuna: I'd better go get him.
So, Yuna has to try and sooth the Gallimimus from running away from his flock.
Princess Yuna: Come here. That's it. That's a good boy. No, no. Wait! Where are you going? You don't walk away and don't want to be... (noticing Vice Principal Luna) alone!
Then, the whole of all notice her on the track, as well. The screen then shows Yuna and the whole team as they get closer to a distance from the track, while the Gallimimus ran back towards the town. Yuna noticing that Luna has her racing tires on her old cart.
Princess Yuna: What are you doing with that old racing kart?
So, the screen does a closeup of Luna's side to show us one of her racing tires. It then moves to on the road to show her still standing there. Then, Luna sighs heavily.
Princess Yuna: (whispering) Come on, Luna, drive.
At last, Luna looks towards the end of the track, then revs her engine. Yuna then smiled as the camera does a closeup on Luna's front of her kart, the lining on her kart and side, her rear, and her front and eyes, and she then sets off. Yuna then watch her happily. Luna drives along the hillside beside the first curve. As she drives along the next straight, Yuna get shocked as she comes towards the final curve where she slid off before. Luna then does an opposite lock, where she turns her body to the left, and turns her wheels right while going around the curve perfectly. Luna then stops as he approaches the finish line, with the dust covering the camera for a few seconds until it shows her looking happy.
Vice Principal Luna: (sighs heavily) Yeah.
Princess Yuna: (coming towards her) Wow! You're amazing!
Vice Principal Luna: Oh, Yuna, I barely notice you watching me! You really think I'm that amazing?
Princess Yuna: Yeah!
At the shed, Yuna started talking with Luna.
Princess Yuna: I mean seriously, you are incredible!
Vice Principal Luna: That's a wonderful compliment you said back there, Yuna, but I'm not the athlete I use to be anymore.
Princess Yuna: But why, Luna? You still got it.
Vice Principal Luna: It's not as complicated as you think it was for me, Yuna.
Princess Yuna: How come?
Vice Principal Luna: Because I wasn't always the best, (showing the video) look at this.
As her videos of her years as an athlete, another one shows about her tragic accident.
Princess Yuna: Oh, right, your big accident.
Vice Principal Luna: I was taken to the hospital for quite sometime, my sister was the only family who cared for me. Come on, I'll let you spend the night at my home.
So that night, Luna told Yund about what became of her during that time.
Vice Principal Luna: After my big accident, I had to be sure I don't work myself too hard to be back on top again. I haven't been the same since my teenage years, ever since I became vice principal.
Then, Yuna was thinking about Doc Hudson a.k.a. the Fabulous Hudson Hornet had a biggest wreck in 1954.
Princess Yuna: Listen, Luna, I know how you feel.
Vice Principal Luna: You do?
Princess Yuna: Mmm hmm, Doc Hudson, the Fabulous Hudson Hornet was living in the past that he couldn't forgive and forget until Lightning McQueen came to Radiator Springs.
Vice Principal Luna: That's very considering of you, Yuna, thank you.
Princess Yuna: Think nothing of it, Vice Principal Luna, that's what friends do.
With that said, they appreciate each other despite their own differences.