What's the difference?
This is not as obvious as we all thought. There are situations and places in which we use these regularly, but there are others where we can understand their use. So...
We will start with steps.
These are a series of surfaces that go up or down, and which we use by putting our feet on them and then move in the direction we want – that is, of course, up or down. For example, if you wanted to climb all the steps of the Eiffel Tower (the verb is to climb when going up, but you can go up or walk up the steps if you want), you would have to go up 1,710 on them. The collective noun is a flight of steps. And when you go down, you do just that - down the steps.
With stairs (or a flight of stairs), we usually think of these as a set of steps that are inside a building (and as a result we usually think of a flight of steps as outside) and that go from one floor to another. So if you were to go up the longest flight of stairs in the world’s tallest residential building, this would be the Eureka Tower in Melbourne, Australia, with 556 apartments, 92 storeys and 3680 stairs.
However… (No, no, please, don’t tell me there are exceptions!)
Sorry, there are. Where shall we start?
A stair, or even a stairstep is one step in a flight of stairs, which can be inside or outside, as long as it links two floors. A staircase or stairway is one or more flights of stairs (or steps) leading from one floor to another. Again, this can be outside or inside. But if it is part of a building that contains the staircase, then it is called a stairwell.
So if you wanted to walk up the world’s longest set of stairs using the definition of both outdoors and indoors – a staircase or stairway - then the winner is Mount Niesen in Switzerland, which has a 3.4 km staircase with 11,674 steps (the same as climbing the Empire State Building more than seven times), climbing from 700 metres to 2363 metres at the top. But don’t all rush to walk them – they are open only one day a year for the world’s longest single-staircase race where up to 500 participants take part. The record is 1 hour and 2 minutes for men, and 1 hour and 9 minutes for women...