The person or persons who see you off the premises is primarily doing this out of courtesy. In their mind the interview is over but it obviously isn't over it in your mind. Once again, do not be tempted to continue conducting the interview as you leave the building.
Even if it is patently obvious to you and others that the job is indeed yours, the approach that you should be following is one of conservative prudence as reflected in your demeanour and topics of conversation. Don't dare give your opinion about what you thought the interview was like from your point of view.
Only if the person escorting you asks your opinion or presses you for an answer, should you comment on the interview at all. If you are forced to comment then be brief and positive. You can say something like, "I thought that the interview went quite well." This answer also gives them the impression that you thought that it could have gone even better.
What you should talk about are things of a more social nature or obvious topics of conversation that are presented to you by the environment that you find yourselves in. It is quite acceptable to comment on the good condition and/or design of the building you're in. Don't make any remarks or observations of a negative nature about anything that you choose to speak about. Instead, be selective and only positive about what ever you have to say.
Don't say anything that may lead them to believe that you think that the job is yours. Doing so will only create a negative impression that will damage your chances. It will be perceived as being presumptuous and arrogant to be asking things like where exactly you will be sitting or where you can hang up your coat.