I see that both towers of London's Tower Bridge have multiple floors but my searches do not show anything specific about how their floor space is used. Is it all accessible for tourists? Or does it also accommodate some bridge-related offices etc.? Is there a plan documenting use of each floor?
The inside is not as big as you would think, the base of each tower holds the huge mechanisms needed to lift the bridge up for passing boats. Replicas are found in tourist spaces above so you can see what this looks like. They do 'Behind the scenes tours' according to their website which lets you see more of this actual area.
The south tower holds a viewing room where they play videos showing the history of the tower itself. Displays are found through the rest of the spaces in both towers.
The two walkways in between have glass floors and are probably the most popular part of the tower experience itself, due to the views.
The North tower has a large lounge available for private hire, but I believe that is not accessible to normal tourists. Again, there are displays and such around the tower.
For security reasons there is likely not to be an up to date fully detailed plan of the layout of the space.
In part the towers contain stairs and (more recently) elevators to access the upper-level walkways. The base of each tower contains counterweights and hydraulics used for opening the roadway, which is still done reasonably often to allow ships to pass. The upper-level walkways were closed to the public in 1910 but re-opened in 1982 as part of the (non-free) Tower Bridge Exhibition. You can also see the steam engines that were originally used for opening the roadway. (Replaced by electro-hydraulics in 1974.)