how long a fall is it - just down to the stair steps or at worst the floor directly below - or is it like an open stairwell going down several stories? If the former, I don't know if Id worry about it as they are pretty agile and have an incredible ability to position themselves in such a way to land safely.

If its an open stairwell though or gaps between steps and the wall where he could get stuck or fall down much further then -yeah, close it off somehow.

At first I was thinking perhaps some kind of round handrail along the top but upon further reflection a feisty kitten might climb and walk on that anyway like a tightrope which would be more dangerous and slippery than just a simple flat platform that they can get a good foothold on. If its a flat platform then perhaps carpet it to make it more secure for them and allow a better grip.

Im no help at all, am I! More questions than answers - good luck!

It's not a crazy long fall, just a flight, but still my cat sprained his ankle once just from falling off a book case onto carpet. The only thing I have been able to think of is to put up some kind of short railing made of either white wood spindles or plexi glass in the middle of the ledge, with moldings on both sides of the railings at an angle so that doesn't become a new ledge. My concern with that is like you said that it might just create a new more dangerous ledge still on top.

I know if I just leave the ledge how it is now he is likely to hang out on it all the time, and sooner or later will either miss jumping up and fall or roll over when he is sleeping or grooming himself. He almost has done that a few times in one of his fav spots which is sitting on our DVR on top of a book case. Luckily my husband noticed and stopped him. That's with a much safer fall and a much wider base.

And unfortunately the just watch him approach won't work, because we want to move his litter box there and my husband has encouraged him to do crazy adventurous things and spots him, so now when we're present he thinks he can do anything and not get hurt. So he is actually more prone to attempt dangerous stunts when we're there.

Ah I see. Those dang cats - if you make it more challenging it becomes even more fun!

I guess the only thing something vertical and very narrow so he cant sit or walk on top of it, and tall enough so he cant jump over it - a plexiglass or metal mesh panel minus a top railing is the only thing I can think of and could perhaps be done in such a way that it could be removed in the future. Or keep the ledge but cover with sticky papert so he learns not to go up there?

Maybe a short wire railing? I can't find a picture but envision 8" metal post with holes that have tension wires running trough. Something l this but much shorter of course.

Here is a post that deals with the same problem but kids not cats. I didn't read all of it but it might have some ideas. [Bannister[(https://www.houzz.com/discussions/what-to-place-on-top-of-bannister-dsvw-vd~806367)

Is it possible to just place plexiglass across the top, and stop it just short of where your head clears as you go up/down the stairs? It's difficult to tell from the pic if you have the clearance since the stairwell may not be a long as it looks. If that idea works, you could then place something along the open edge to keep him from accidentally walking off the plexiglass.

Otherwise, some type of contemporary railing that goes to the ceiling (as shown in the Bannister link) would definitely work.