From the Super Mario Wiki
Star Hill is the name of a mystical hill in the Mario series. Its appearance and function differs in the two games it appears in, and shares its name with a third location. In Super Mario RPG: Legend of the Seven Stars, it is made out of many smaller hills, which look like dark blue meteorites. In this appearance, Star Hill is literally the place where wishes come true, scattered around the ground as Wish Stars.
In Paper Mario, Star Hill is renamed Shooting Star Summit in the English version, although the name remains the same in Japanese (Hoshi no Furu Oka, meaning "Falling Star Hill"). In this game, the area is a mountain north of Peach's Castle, and while stars are still found on the ground, they are not Wish Stars, but merely fallen shooting stars of various colours. As well as being lauded for its beautiful view (Mario is even advised by a Toad to take Peach there on a date), Paper Mario's Shooting Star Summit is notable for being the closest place to Star Haven, which can be accessed from the hill via the Star Way.
Super Mario RPG: Legend of the Seven Stars
In Super Mario RPG: Legend of the Seven Stars, Mario, Mallow and Geno travel here for a Star Piece. This Star Piece is the only one that can be taken without a fight; it rests on the ground at the end of Star Hill, unguarded by anyone (most likely because the player fought in Booster's Tower and Marrymore). The Wish Stars can be examined to hear the wishes of the people who made them. Two of these wishes will come true over the course of the game, and if the wishes are examined after it comes true, the wish will be changed.
It is impossible to traverse the entire hill simply by walking; the only way to access different areas is by lighting several of the unusual star-shaped flowers, causing a keyhole in a large star in the area to grow. Going through the enlarged keyhole allows the enterer to travel to another area instantly, and the keyhole shrinks behind them.
In Paper Mario, after Bowser takes Peach's castle to the sky and easily KOs Mario, Eldstar notifies Mario in a dream to head to the summit for counsel. Once he has awakened from his unconscious state after many days and Goombario's family revives him, he heads to the summit. Once he arrives, all seven Star Spirits appear (using the last of their power to create the projection) and reveal to Mario he must rescue all of them to save Princess Peach.
On his way back down the mountain, Mario is introduced to Twink, who gives him the Lucky Star from Peach and teaches him how to use the Action Command. A Magikoopa then appears, having followed Twink to Mario, and must be defeated.
When Mario has saved all seven Star Spirits, they use their power to open a portal atop the mountain to Star Way, which leads to Star Haven. At the base of the hill lies Merluvlee and Merlow's house, where Mario can have his fortune told and trade Star Pieces for badges.
Names in Other Languages