Trying to find a book with a cube planet

Question

I'm trying to rediscover a book I read as a preteen/young teen, early 2010s. Though I don't think it was new at the time.

The plot I remember involves the protagonist (a young girl I think) and her friends traveling to the edge of her cube planet before making it to one of the other sides. They don't know the planet is a cube, but think it's flat and are trying to find the edge of the world. The edges of the planet were covered in sharp crystal structures. On the way they find a crashed spaceship, though it's not identified as such by the characters since they live in a society that hasn't made it to space yet. In the ship they find and activate an robot/android. The robot is the one who explains the planet is a cube, as they crashed due to their systems crashing when they tried to process the existence of an impossible cube planet. The different sides of the planet had never interacted with each other due to how hard it is to travel between sides, so the culture on the other side was completely different, though I don't remember either the new one or the one they started in.

Otherwise the only thing I really remember is that gravity worked as it would on a cube, so the closer the protagonists got to the edge, the stronger the gravity pull becomes trying to drag them back to the center of the side.

I'm Swedish and read it in Swedish if that helps, but I don't know if it was originally in Swedish (not likely imo, there's very little Swedish written scifi). I think it was the first of a series, but I never read any more.

You'd really think a book about a cube planet would be easy to find but nope!

EDIT: The fact that the planet was a cube wasn't a big deal untill the end of the book. Before the spaceship encounter everyone thought the world was flat because to their observations, it was.

Answer 1

I believe this is Terra Hexa by A. R. Yngve.

Henna and Gala's first night in the new world is cold and clear. The stars shine against the dark sky and beyond the horizon, on the other side of the great desert, cities loom. The new world is far, far bigger than they could have ever imagined and contains dangers of a whole new kind. They have barely had time to leave

I read the book Terra Hexa in Swedish when I was in my early teens, somewhere between 2007 and 2011. I have one clear memory about a chapter in the end of the book where the protagonist and her friends traveled to the edge of the world. On their journey they noticed that the gravity was pulling them back towards the middle of their world. I think it ended on when they discovered the edge and saw the other side of the planet, a world they had no knowledge of before. The closer they got to the edge the more "chrystals" appeared and they discovered their planet was made out of diamonds.

Found a blurb in Swedish on Fantasyhyllan that fits the description more:

On the way up, she saw the sun in the sky, to her left—much, much brighter than she had ever seen it in her life. Its light shone white instead of yellow—she couldn't look directly at it, even with the Goggles. The sky was a very dark blue and the cliff face seemed unnaturally sharp in the harsh sunlight. Up and straight ahead the world ended. Winds howled and made strange noises, and she almost thought it sounded like a chorus of ghosts trying to scare them away: Oooooh.. . ooooh... She could see the horizon!"

A journey to find the horizon! Henna and Gala, two inseparable sisters, have grown up in a land where the sun literally never sets. Together with their friends, they set off on an expedition to the end of the world. Many adventures later, the intrepid explorers arrive at their destination—and discover that their world is much larger than they ever imagined. About to be captured by the Ostrich Riders and sold as slaves to the Golden Man, it takes both Gala's cunning and beauty and Henna's wisdom and courage to save them...

(via Google Translate)