The Mass Rock (Carraig an Aifrinn ) is in the Grounds of the Ballybrit Racecourse, in the Parish of Castlegar, Galway
Coordinates; 53.297481 , -8.996602
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Where is it? Just North of the old Tote, and immediately South of the Race Track.
During the Penal Laws, where going to Official Mass was outlawed, Locals would assemble at this place, covertly.
^Pope John Paul the second, blessed this Rock, during his Papal Visit to Ireland (and Ballybrit), in 1979.
Additional reading; http://galwayindependent.com/20130403/news/ballybane-in-hard-times-S1107.html