Ryuudou Temple

A mountain temple on the outskirts of Miyama.
As the name suggests, it functions as the keystone of Fuyuki's leylines, and could be said to be the very heart of the city.
The temple's mountainside lake is an official Holy Grail summoning site, and beneath it lies an enormous cavern.
Incidentally, the giant cave-in after the epilogue of the Sakura route took several years to recover from.
…Also, as it turns out the primary reason for the cavern's collapse was not the destruction of Angra Mainyu, but rather Rin's overenthusiastic rampage.
Way to go, Issei.
To instantly recognize Rin as an enemy of Buddhism, you truly are worthy of being Ryuudou Temple's successor.

Fate/side material: Fate Encyclopedia