I vaguely remember details about the book. I remember that travel between dimensions was regulated by either a company or government entity, and they used a box shaped hallway, basically a tesseract that had stretched infinitely in many directions forming a type of hallway with windows that could peer into those dimensions. Using controls, they could then enter those dimensions. One part talked about a "vacation world" where one of the characters had set up a house with a bunch of primitive life forms that inhabited it. I don't remember too much more as I never finished the book due to its size and time constraints at the time, although I am wanting to find it and start reading it again.
I believe that the town where they housed the interdimensional gateway at was in a mountain region, but it's been quite some time since I read the book. I do remember them briefly mentioning that Sherlock Holmes was real in one of the realities when describing some of the aspects of the multiverse.