Sounds like a question for a glass specialist.

This is SO not a DIY job!

I am so curious about this post... You have a well opening in the main corridor of your house? How? And also, you want it to remain visible by using glass to cover it? Why??

Again, merely curious I have no advice of value to add here.

Just to say that a friend's old house had a well in the kitchen!! They placed glass [or something else] over it....

I'm not saying it's uncommon. I'm saying that floor people aren't likely to be glass experts. I've seen it done on some stair mid-landings and elevated walkways. Pretty cool.

A professional on houzz writes: "The glass floor has a "frit" on it to make it non-slip, more scratch-resistant and also not as transparent." - PRO/ WA Design Architects

[https://www.houzz.com/photos/willits-compound-industrial-hall-san-francisco-phvw-vp~673585[(https://www.houzz.com/photos/willits-compound-industrial-hall-san-francisco-phvw-vp~673585)

Following!

I'm a cautious approacher about spending, and I also investigate some first!! I get the chat, and information gathering... have a good project!

Sophie, I appreciate your concern. I'm not so sure the glass supplier knows what he's doing since I checked with four different businesses and half quoted a price of 5000 eur for a monster mix of glass layers, the other half quoted 1/10th of that price for a three layer glass sandwich of 30mm thickness. Who's right and who wants to make money, I don't know, so I'm trying to get a second opinion by people who I'm hoping know more than I do.

Have to say, sometimes I feel that way about medical doctors!

Wow! I've never seen anything like that except in a boat. Not sure where you are located, but maybe the glass bottomed boat people would know.

we *wished* we could have done this! when we added a room to our 1870 house, first day of the project the excavator dug up an amazing brick cistern not far below ground level. sadly, it was where the footings had to be. had it been in the center of the room we SO would have put glass over it and illuminated it!

"How could you start a project like this without informing yourself? It's your own fault you got taken advantage of."

"Let the pros be the pros, don't worry your pretty little head about it."

What's an interested home owner to do??

(not directed at you, Louis John)

I've seen a transparent walkway sunk into the floor at a natural history museum, with an underwater display beneath it. There's an off chance that would be a useful place to ask about this. It's unlikely a tour guide or such would know, but maintenance might or admin could possibly get you in touch with the builder. Just a thought.

Another idea might be to put out a call on Facebook or other social media. A friend of a friend of a friend might have first hand experience!

Found this online.

Well Masters are the UK’s leading well restoration specialists that offer a complete service from well cleaning to glass well covers and light installations.

The modern alternative to the traditional well top is to have lights installed into the well and then a glass cover over the top. Glass well caps are great for both indoors and outdoors.

Glass well covers are the best way to enhance the well head for both practical and safety aspects of the well plus also add a huge safety aspect to the well.

Not only do glass well covers look amazing they are also extremely safe. On average the glass has 3x 10mm thick laminated toughened glass layers all bonded together forming an extremely strong glass well cover which can with stand a car driving on it. If the glass was to ever get damaged in anyway then only one layer would get damaged leaving the well still safe until maintenance could be carried out. Having said that glass covers last many many years.

A glass well top will also allow you to still use the well with the installation of our pump system which can be installed so it does not draw you from the beauty of the well. By using black pipe work, black rope, black cable, black fittings and some careful positioning, the look does not diminish from the character of the well.

Condensation can be a major problem with a glass well cover so please do not leave it for anyone to install please contact us because we have many, many years experience and can ensure your glass is condensation free forever. Once it is all installed it is usually impossible or extremely hard to put right so please contact us before contracting out to a builder or trying to install yourself because it will be a very expensive mistake and will look very ugly.

There are a few glass manufacturers who can claim to supply a glass cover with an anti-condensation film. Please DO NOT pay for this option. There is no such thing as anti-condensation when it comes to a well and a glass well cover. There is many chemicals which can be put on the underside of the glass which make the water drip off rather then stay on the underside and this is what you would be paying for. The actual cost of the product is £3 for a large bottle! You will still get drips from it and it will still look extremely horrid. The only way to stop condensation is by contacting us and let us supply and install your glass well cover. A well is a constant temperature where as outside air changes all the time so no matter what you do to treat the glass you will get condensation.

For those following, I found this article which clears up some doubts: https://www.glassonweb.com/article/how-strong-are-glass-floors 

No no no no no!! Just the thought of glass covering a well where I might walk makes me nauseated and vertiginous. Please make sure you inform guests about it, before someone comes upon that area unexpectedly and has a heart attack.

Cool idea. Just not for me!! ;-D

Yes yes, thankfully we're not all going to feel a-woozy! My friends' covering had no effect on them, and they were natural, physically comfy people... :)