The Town That Were Pubs is only pubs. There are no streets. There are no houses. There are only pub.
Sailors talk about it in hushed tones.
There are windows. They look out onto a starry night and an endless sea of rooftops. The rooftops all belong to other pubs. Some of the rooftops are pubs in their own right. You can, in the distance, see a moonlit ocean. You cannot reach the moonlit ocean. Feel free to try though. Many a debauched evening has been spent in fruitless quest for the moonlit ocean.
The food is very good. Most pubs have a speciality or two. There is a great deal of rivalry between denizens of neighbouring pubs.
The bar staff all seem like normal people, but you have never heard of anyone you know being hired as one. The don't answer inconvenient questions about how it all works, but they're not dicks about it.
Most good pubs and all bad ones have a secret entrance to the Town That Were Pubs. You can of course only access the secret entrance when you are too drunk to remember where it is. Whenever players carouse they have a one in a thousand chance to wake up in the Town That Were Pubs.
You meet all sorts of interesting people in the Town That Were Pubs. Viking chieftains, Tang Dynasty poets, Nantucket whalers and labourers fresh from cutting stone for the Pyramids. Also wizards and elves and bug-eyed guys from Tatooine cantinas. The Town That Were Pubs respects no boundaries of time and space.
You can leave the Town That Were Pubs the same way you entered it - by getting so drunk you can't remember where the secret exit is. This generally happens if you hang out in the Town That Were Pubs long enough. Say for about an adventure's worth of time, or long enough to have a chat with an interesting stranger and find out a single important piece of information. When you leave you will not necessarily find yourself at the same point in the space-time continuum where you entered the Town That Were Pubs. Your memory of everything that happened within will be clouded by alcohol, and probably seem like a crazy dream.
Some scholars say that there exists an equivalent to the Town That Were Pubs for every different kind of building - that there is a Town That Were Libraries and a Town That Were Slaughterhouses and a Town That Were Post Offices and a Town That Were Public Toilets. Those guys are dicks and you should ignore them.