Would the Voth city-ship be able to hold a Borg cube inside of it? It's obvious it would be able to hold hundreds of Galaxy-class ships or even a few Deep Space Nines, so would it be able to fit a Borg cube?
On Memory Alpha, a Borg Cube is described as:
(Which would be each direction)
Whilst Memory Beta says the Voth City ship measured over 4.9 km in length.
Looking at this size comparison chart, we see that the Borg Cube is substantially taller than the Voth City ship:
This picture comparing the two (to scale) should help to answer
These images are from the excellent Jeff Russells Starship Comparison Guide
The figures used to create these images to scale are from Memory Alpha - citing the Cubes size as
VOY: "Dark Frontier"
And Memory Beta - citing the Voth City Ship as 4,900m long
Even though this only confirms length, the to scale drawings show clearly that the Borg Cube would not fit inside the Voth City Ship as it is too tall.
For Deep Space 9 - you might be able to squeeze 1 DS9 into the Voth City Ship if you got the angles right, (and if the Voth City ship is wider than it is tall, which it appears to be). Or many more if you took the pylons off/pushed them down.
Size of DS9 as given in Memory Alpha