(Thank you very much to 'Yan Yu Jiangnan', 'Lei Xiang', 'Ice Feather ↑↓ Weinuo', and 'Phoenix Dance in the Sky of Anime' for their rewards!)
In Gensokyo, whether human or youkai, people generally used the simple term "mountain" to refer to Youkai Mountain.
In other words, whenever someone mentioned the mountain, they were most likely referring to Youkai Mountain.
Many ancient youkai and gods lived on Youkai Mountain, where a cultural society distinct from those of other humans and youkai had also been established.
Aside from the gods who were rarely seen in daily life, the youkai active on Youkai Mountain were mainly tengu and kappa.
The tengu and kappa possessed high-tech methods comparable to those of the outside world. This was a special society formed long ago on the foundation of one established by the Onigami who led the tengu.
Thus, countless youkai had lived on Youkai Mountain since ancient times, and the youkai residing here generally had a longer history than the humans of Gensokyo.
Precisely because the youkai of Youkai Mountain differed from those below the mountain, living in an independent society and serving as an important point of balance in Gensokyo, especially with the tengu and kappa possessing technology rivaling or even surpassing that of the outside world, no youkai had been able to invade this mountain.
Among them, the tengu were especially famous for photography, printing, publishing books, and similar technologies, while the kappa possessed skills in steelmaking, construction, crafting tools, and more. They were an extremely unique presence in Gensokyo, yet did not seem out of place.
Moreover, the youkai of Youkai Mountain were more cheerful and united than any race in Gensokyo. They lived prosperous, near-futuristic lives with advanced technology, but their strong sense of companionship also made them quite exclusionary toward outsiders.