Deep within the earth, beneath volcanoes and lakes, through tunnels and caves, lies the Undergroundia: a world filled with colorful rocks, rivers of lava, and strange inhabitants like Berbs, Fatoules, Water-Stalides, and Cave Giants!

But what would all this mean to us if one day, in a strange twist of time and moment, a small pebble, Stone, did not get lost in these lands? Searching to discover where he comes from, how he was created, and where his home is, he embarks on an adventurous, thrilling journey in this unknown world, making many friends, but also... cunning enemies!