Answer : 1. "ladder"
Explanation :

Let us explore the given options: '

A ladder is a piece of equipment consisting of a series of bars or steps between two upright lengths of wood, metal or rope used for climbing up or down something. 

'Steps' are flat surfaces, especially in a series, on which to place one's foot when moving from one level to another. 

'Stairs' are a set of steps leading from one floor of a building to another, typically inside the building.

 'Railing' is a fence or barrier made of rails. 

Hence, the correct answer is option 1.