Trinity College Dublin (TCD) generated almost €12.7m from its Book of Kells exhibition last year.
More than a million visitors paid to view the ancient manuscript.
The revenue generated from the Book of Kells and Old Library tour, which works out at a weekly average of €244,230 for the 12 months to the end of September 2019, almost equals the €12.8m it generated from accommodation across several Dublin sites last year.
The book contains the four gospels in Latin and the manuscript's celebrity derives largely from the impact of its lavish decoration and artistry.
It has been on display in the Old Library at Trinity College from the mid-19th century.
Entrance tickets to view it range from €11 to €14 for adults, while family tickets cost €28.
Recently published TCD accounts for 2019 showed six academic medical members of staff last year earned more than €300,000, with the top earner receiving between €360,000 and €370,000.
It comes as the college said it is freezing recruitment as the financial fallout from the Covid-19 crisis hits.
While there will be some exceptions, hiring will be allowed only on a "case-by-case basis" and where a "strong business case can be made".
Trinity HR director Antoinette Quinn sent an email to heads of departments yesterday advising of the decision.
It refers to the Covid-19 public health emergency, saying: "It has become clear that there will be a significant financial consequences for Trinity in the coming years."