As shown in the series, the SSSP Japan Headquarters that appeared in Ultraman looks so quirky that it remains unforgettable while it is shaped like an inverted pyramid.
Given possible attacks from outside, the underground base of the TDF of Ultraseven looks much more realistic, but the modern-looking SSSP building seemingly equipped with cutting-edge technologies was also attractive enough to amaze us kids back then. (And I do love the sort of idyllic depiction of the SSSP and their behaviors.)
As a matter of fact, it is known that this building was designed by Tohl Narita allegedly on the model of (or inspired by) a real-life seminar house building associated with a university in a suburban area of Tokyo.
While it is also known you can see the inside of the seminar house building in Ultraman Episode 11 where a press conference over the strange meteorite which fell down from space was held as the stone was capable to substantialize someone’s thought (the exterior is a different building).
The exterior of the seminar house briefly showed up in Episode 47 of Kaiju Booska as an institute of a scientist funnily named Dr. Kaminari (thunder), and this inverted pyramid shaped building still seems to exist even now.
As you know, the stage set was regularly applied to the interior of the SSSP Headquarters, it is said that the set walls were sloped just like the exterior set of the building although it is unclear through the screen, and they say the slanted walls often made the cast and crew members feel odd.
The SSSP interior set also shortly appeared in Kaiju Booska Episode 8 as a satellite observatory.