I wrote to Tim Berners-Lee after exploring CERN last week, looking for the location where the web was invented, his replies regarding the exact locations are below (I’ve put up photos of the excursion as an Oobject list, here ).
[ Update, Jan 2012: One of the more interesting consequences of the details below, that hasn't been picked up anywhere, is that technically the web was invented in France, not Switzerland.

The blue marker on the map above shows building 31. Note where the border is.

I'll bet if you asked every French politician where the web was invented not a single one would know this. The Franco-Swiss border runs through the CERN campus and building 31 is literally just a few feet into France. However, there is no explicit border within CERN and the main entrance is in Switzerland, so the situation of which country it was invented in is actually quite a tricky one. The current commemorative plaque, which is outside a row of offices where people other than Tim Berners-Lee worked on the web, is in Switzerland. To add to the confusion, in case Tim thought of the web at home, his home was in France but he temporarily moved to rented accommodation in Switzerland, just around the time the web was developed. So although, strictly speaking, France is the birthplace of the web it would be fair to say that it happened in building 31 at CERN but not in any particular country! How delightfully appropriate for an invention which breaks down physical borders. ]

There is a plaque in a corridor in building 2, but no specific offices are indicated and there is some ambiguity as to what happened where, in building 31. Thomas Madsen-Mygdal has a gallery showing locations in building 31 and 513, but there are very few places on the web documenting these places. I took photos of the plaque, such as the one here, with Creative Commons licenses, so that they could be used elsewhere.

The reason I’m interested in this is that recognizing the exact places involved in the birth of the web is a celebration of knowledge itself rather than belief, opinion or allegiance, both politically and spiritually neutral and something that everyone can potentially enjoy and feel a part of.

Secondly, many places of lesser importance are very carefully preserved. The place where the web was invented is arguably the most important place in 2 millennia of Swiss history and of global historical importance.

Lastly, this kind of information is perhaps overlooked as being so obvious as to be common knowledge, exactly the sort of thing that sometimes gets forgotten. I’m not suggesting that the locations have indeed been overlooked, but they are not preserved or all indicated and the people I spoke to didn’t know the full details. So just in case…

DG: Where were you (at CERN and which building/rooms or home) when you thought of or were writing the original proposal for the web in 1989?

TBL: I wrote the proposal, and developed the code in Building 31.
I was on the second (in the European sense) floor, if you come out of the elevator (a very slow freight elevator at the time anyway) and turn immediately right you would then walk into one of the two offices I inhabited. The two offices (which of course may have been rearranged since then) were different sizes: the one to the left (a gentle R turn out of the elevator) benefited from extra length as it was by neither staircase nor elevator.
The one to the right (or a sharp R turn out of the elevator) was shorter and the one I started in. I shared it for a long time with Claude Bizeau.
I think I wrote the memo there. [ dg: proposal for the web was written, i.e. web was 'invented' in room 2-010 ]
When I actually started work coding up the WWW code in September 1990, I moved into the larger office. That is where I had the NeXT machine, as I remember it. [ dg: larger office, i.e. where first web server was and software was written, where web was 'created', is room 2-012 ]
The second floor had pale grey linoleum, the first floor, where Peggie Rimmer had her office, had red lino; the third floor had pale yellow lino. The ground floor had I think green lino. Also on the second floor was the Documentation et Données, later Computing and Networking, HQ with David Williams at one point heading it up.

DG: For the development of the web, can you remember which offices were used in building 31 or off the corridor shown in building 2 in the attached image?

TBL: Building 2 I never had an office in. Robert Caulliau did, and various students, including Henrik Frysyk Nielsen and Hakon Lie, and Ari Luotonen, worked there.

DG: Was some of it inspired at home and was that here: Rue de la Mairie, Cessy (France)?

TBL: My house was [exact address removed since people live there] Rue de la Mairie, but I rented it out for some time around 1990 and actually lived in Les Champs Blancs, Chavannes de Bois [Switzerland]. But then we moved back to Cessy for a year before leaving.

[ Update: I went back and took some pictures (Creative Commons license so you can use them) of the room where TBL created the original proposal for the Web. And have some exciting news to share about it soon! ]

Door to the room where the web was created

The Polish coder who currently occupies the room didn’t know its significance. He was very happy to find out.

Ben Segal who helped setup the original web server in the room where the web was created