In the centre of a vast, level plain, a huge cubic structure is visible.
As the traveller approaches, they are overwhelmed by its size.
On reaching the cube, the traveller notes that it is surrounded by other structures - spheres, cones, pyramids and cylinders - which would be in other contexts
be judged very large, but are dwarfed by the cube, which is 1000m along each edge.
Having paid their entry fee, the visitor is admitted to the facility. The larger shapes are hollow, and contain informative galleries, as is the cube, which has painted on one face the words "ONE CUBIC KILOMETRE" in a number of languages.
The cube itself is empty, but well-illuminated. It is simply a vast, enclosed space, which is staggeringly big. The floor is used for various exhibits; here, you can see, in a circle, a ton of sand, of concrete, iron, and wood, with representations of a ton of gold, silver, uranium, platinum, lead and iridium.
In the centre of the circle is a tank containing a ton of water as a standard reference.
In a similar adjacent circle are a ton of potatoes, corn, wheat, yams, coconuts and other foodstuffs, again with the central water tank as a reference.
There will be divisions for different subjects; biology, astronomy, physics, chemistry, economics. As far as possible, everything will be "actual size" - one of the cylinders outside will be representative of the volume of JP-1 used by a transatlantic airliner, another the volume of gasoline consumed by an average driver in their lifetime. A pyramid would show how big a heap the population of China would be if they were all piled up in one place.*
Some of the structures would contain hotels, as the site will be too large to see all of it in one day.
Golf carts, travellators and other mobility devices will be provided, but visitors will be encouraged to "walk the cube" if they are at all capable of it. It's only 4km, after all.
At night the structures will be floodlit, but these floodlights will be switched off when the astronomical observatory on the top of the cube is active.
Camping is permitted on the top of the cube.
* Hopefully this will be done using the actual population of China, altho there apear to be a few Issues to resolve in the implementation.