Holy Site Prayers is a project in Civilization VI. It becomes available after building a Holy Site district (or one of its replacements).
While this project is underway, the entire city is dedicated to holy pursuits, converting 15% of its Production output to Faith. When completed, it yields Great Prophet points equal to approximately 22% of the Production invested in it (on Standard speed).
In Gathering Storm, this project also increases the Religious Pressure emanating from the Holy Site by 100% per turn if the city has a dominant religion.