It's walkable, but you can't see the "sun" from the "earth," and it's walkable in well more than an hour, at which point I don't think that you're really keeping the scale in mind.

We can always look at images or whatever if we want to get an intellectual sense of the scale of things. I think the advantage of a model is that you feel immersed in it, and I don't think you do at this scale.

It's challenging! It's hard to find a location and a scale which gives you this human sense of the sizes involved. At most scales, you have to make the planets pinpricks in size. But, especially for the inner system, you can make it work.

EDIT: Here's I think something that works.

https://www.youtube.com/watch?v=zR3Igc3Rhfg

For a better perspective on scale, they should do a model where in 1 place you have the sun, its planets, asteroid belts etc, and (to scale!) in a 2nd place you have a model representing the nearest star system (Alpha Centauri).

Oh... and of course put in where Voyager, Pioneer & New Horizons probes are these days - after 40+ years of travel at ~15km/s.

I think this is near-impossible. The diameter of earth is about 12,700 km. So if the distance between the Sun and Alpha Centauri were "the maximum distance available on Earth," then the scale is 3.25 billion to 1.

The sun's radius is about 696,000 km, so 7x10^6 meters, so at 3.25 x 10^9:1 scale, it's about 2mm across. The planets would all be specks. You could see orbits, though they'd be small. And that's if you place your alpha centauri model literally "on the other side of the world" from your sol model.

I think you can do very slightly better by using great circle distances rather than straight lines cutting through the earth. After all, I think that's what this model is doing.

Sure, it could be half the circumference of the earth instead of the diameter. The circumference is pi times the diameter, so half the circumference is a little over 1.5x the diameter -- the sun could be 3mm across instead of 2mm.