Spirits are everywhere in this world. Since this school was built on the site of a former shrine, they tend to gather here especially.
Literal
Spirits [topic-は] this world [possessive-の] anywhere [at-に] are-[honorific-いらっしゃいます]. This school [topic-は] shrine [possessive-の] former-site [on-に] made [passive-られていますので], especially gathering [honorific-になる] tendency exists.
Two keigo-laden sentences about ghosts. The speaker uses honorific language for the spirits — いらっしゃいます ('are present,' honorific いる) and お集まりになる ('honorably gather,' お~になる pattern) — treating them as honored beings worthy of respect. お社 (おやしろ) means 'shrine.' 跡地 ('former site') is common in real-estate and historical contexts. The combination of supernatural content with respectful keigo creates a distinctly Japanese tone where spirits are part of the social hierarchy.