He was climbing up...

[99bottles]

This is the action I want to describe...

https://www.wired.com/images_blogs/wiredscience/2009/08/i_tunes1.jpg

Here what I've got so far.

He was climbing up between two opposite (or opposing?) walls, with his palms on one and his soles on the other.

Is it natural enough? Approve it or improve it, chiefs -- I'll be grateful either way.

 

[Tarheel]

I don't get it. You can climb over a wall. But I don't know what it means to climb between walls.

 

[Tdol]

There may be a term in parkour for it.

 

[99bottles]

I don't get it. You can climb over a wall. But I don't know what it means to climb between walls.

Did you click on the link I put in the first word of the OP?
Edit: I made the link easier to see.

 

[Jemima23]

Here, I found a video of the guy climbing up the walls, you can listen to the way he describes it in his tutorial:

 

[emsr2d2]

I'm sure the people who do such activities have a perfectly good word for it but I don't think non-participants want/need one.

 

[Tarheel]

Wow! First, that's not normal at all.

They say "Safety first." Are you kidding me? If they were concerned about safety they wouldn't do it.

It's not normal climbing, and I don't have a good word for it.

Some people have way too much time on their hands.
;-)

 

[99bottles]

I'm sure the people who do such activities have a perfectly good word for it but I don't think non-participants want/need one.

Then there is no point in using a term most of the readers won't understand. I should describe it in a circumlocutory fashion. Is what I wrote in the OP natural English?

 

[Tarheel]

It's understandable that it's hard to describe, and I couldn't visualize it until I saw the video.

Is there some reason you need to describe it? Maybe you just want to see if you can?

I don't know how I would describe that. Maybe I would start off by saying "It's like nothing you've ever seen before." (That would be true for most people.) Then I might say, "It's climbing, but not in the usual sense of the word." And then I might say, "Oh, never mind! Just watch the video."
;-)

 

[99bottles]

It's understandable that it's hard to describe, and I couldn't visualize it until I saw the video.

Is there some reason you need to describe it? Maybe you just want to see if you can?

I don't know how I would describe that. Maybe I would start off by saying "It's like nothing you've ever seen before." (That would be true for most people.) Then I might say, "It's climbing, but not in the usual sense of the word." And then I might say, "Oh, never mind! Just watch the video."
;-)

Forget about the video. Click on the link in the OP. It's just an image.

 

[5jj]

The video is rather more helpful than the static image for people who have not encountered this activity.