Doesn't look as if it would take much to beat it...
The floor is on the level 1 viewing gallery of the Spinnaker Tower in Portsmouth, which, had I thought to take a picture of it, I'd show you. All these times I've come to Portsmouth, the tower has either not been finished, been finished but with broken lifts, or been closed because of bad waether. Today, it was open and one of the lifts was working, so I paid my £6.20 and went up. The glass floor is on viewing gallery 1; viewing gallery 2 gives a higher but less panoramic view, and viewing gallery 3 ("the crow's nest") gives the highest and narrowest view of all. Oh, and it's open to the weather. Still, getting to the top of high buildings addict that I am, I went to all three galleries and took some pictures.
As it happens, the views are pretty good. Look, you can see the Isle of Wight on the horizon:
Here's a view of the Royal Navy's finest:
In case you can't make it out, that's HMS Victory in the middle there:
All in all, I spent half an hour going up, taking pictures, waiting for the lift and going down. Well worth £3.
As soon as I emerged, I saw lightning, then heard the crash of thunder of an approaching storm. Ha! I'd already been up, so closing it for the incoming storm didn't affect me. Whoever arranged the weather was obviously told the wrong time to deliver it.