If the gelatinous cube symbol is actually partly transparent anyway (given you can see the texture of the floor below it), items don't all need adding to the cube. As long as the items exist as symbols, they can simply be put "below" the cube by the map's creator.

On the size element, the "you can drive a cart along them" argument is partly why I suggested seeing the sewers in "The Third Man" movie, because that's where the climactic chase happens, with large numbers of police and soldiers, where there are multiple levels stacked over one another, and nobody has any problems for headroom, and places are up to river-cavern wide in parts. Somewhat like the early London Underground "tubes" (and I'd assume others built around the same time, later 19th century), some of these would have been dug out as trenches, had their surfaces coated with mud/bricks/concrete, etc., and then covered over later where necessary.

@thehawk makes a good point about ancient sewer systems. I think the earliest definite sewer pipes date to around 4000 BCE in what's now southern Iraq, at the ancient cities of Eshnunna and Uruk, although more sophisticated sewer systems survive archaeologically from the Indus Valley civilization around a millennium later (c. 2300-1800 BCE). Most were of brick or clay construction in various forms.

There is a boat at the ferry crossing landing on Ferry Road, but it's a sailboat.

Ferries don't even need to be especially boat-shaped, of course, as something like a square plank raft will do, particularly of the kind that uses pull-ropes to cross the watercourse. Some of those types were still in use in places well into the 20th century (notably the more rural areas, and on relatively narrow crossings). Depends what you need, where and when.

Glad we got that sorted at least! I did know about the hotspot disabling, but wasn't online after you replied yesterday. Thankfully, we always have Monsen 😁!

When you hover over the "Open PDF Mapping Guide" words, do you get a "pointing-finger hand" symbol on your cursor instead of the usual arrow one? I ask, because you mentioned the hotspot does not seem to be active, and that you "assume" this is what you have to do, whereas the change to the pointing finger cursor icon ordinarily confirms it's where you need to click.

I think Adobe took over half a minute to open my mapping guide, but I find the Adobe Reader startup is often pretty slow from "cold" these days. (Too much unwanted and unrequested Windows clutter that keeps getting dumped on my system, I suspect...)

This is based on a download and installation done within the past twenty minutes, incidentally (so around 17:15 UTC on Dec 2).