Well, it always happens this way but I went to Google images and searched for "spa dome" and I sort of found what I was talking about.
There is a "product" from a company called Rizebo at
www.rizebo.com (go to the photo gallery page to see the clear dome). It looks like a one-off that this guy built and plans or planned on selling. From the looks of the pictures, his showroom is in his own tiny backyard. I am going to call the number tomorrow to see if this is actually available. The website looks very amateurish and is unfinished.
It looks like a section retracts into the dome to allow access inside. Pretty cool idea but I know the one I saw wasn't hard plastic. I'd be afraid of this thing cracking or having huge scratches that are amplified by the sunlight.
If I manage to find the one I originally saw, I'll post a link. I could only imagine what shipping would cost to get an 8' x 8' x 4' plastic dome delivered unharmed.