From the Super Mario Wiki
To access the slide, the player has to climb the mountain until they get to the Fwoosh. Immediately behind the Fwoosh is a trail of Coins leading to a secret portal to the slide. If the player loses a life on this slide and jumps back into the painting, they will return to the start of the slide, provided the life lost does not result in a Game Over.
The slide begins with a straight ramp with three dips in it, followed by a turn. After this turn is a long "U"-shaped bend that ends in a fork; continuing on the path leads to a drop that causes the player to lose a life, so the player needs to slide onto the wooden path to avoid it. The wooden path has two gaps in it that the player will slide over and onto a bend. After the bend is a twisted tunnel, which ends at a narrow road. Past this are two final bends ending in a large jump, leading to a room with the hole to the Power Star.
In the original game, the Power Star is in an alcove with a small fence; in the DS version, the fence covers the entire alcove, presumably to prevent the player from dropping in from the ledge above and collecting the Power Star without having to go through the slide, although one can still do so using Luigi's Power Flower ability.
Names in other languages