Yes - The Gates of Delirium

Terrific song and album; not my personal favourites by Yes, but there are so many contenders so it's not too surprising (if I had to chose I'd say my favourite song by them is Heart of the Sunrise and my favourite album is Close to the Edge safe picks, I know...)

I found a YouTube link in your post. Here are links to the same video on alternative frontends that protect your privacy:

• yewtu.be
• inv.nadeko.net
• yt.artemislena.eu
• piped.video