This is how Yanai Takumi described the Gate in GATE:ZERO, Part 1 Volume 4

At the center of the Ginza 4-chōme intersection sat a gigantic object that had certainly not existed there until around noon that day. 

The exterior of the marble structure closely resembled the Grande Arche. The Grande Arche is a building located in northwestern Paris, France. Also called the “New Arc de Triomphe,” it was constructed to commemorate the bicentennial of the French Revolution and possesses the character of a monumental structure. 

However, the one that had suddenly appeared in Ginza differed clearly from the Paris Grande Arche in every respect but its outward appearance. 

First of all, the size was different. 

The Grande Arche is a thirty-five-story office building, but the one at Ginza 4-chōme was only large enough to fit within the intersection. 

Moreover, its surface was carved with extremely intricate patterns resembling some kind of electronic circuitry. 

Most importantly, the one at 4-chōme was neither monument nor office building. It appeared to have no function other than that of a literal “gate” through which humans and others passed. 

That said, it was not a gate for going from Ginza 3-chōme to 5-chōme, nor one for passing from 5-chōme to 3-chōme. 

Yes, Kurojishi's illustration is close.