It's not all that big, actually. The temple is a "cathedral" only in the Catholic Church sense; it's the "cathedral church" of a major player in the Ratri faith's hierarchy.
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It is open to the public, though it has far less of a "congregation," per se, as opposed to supplicants seeking aid from the faith's ecclesiastical fighting order. Warwik City is the center of the Ratrian religion (and the Temple District of the New City has the High Basilica of the faith), and there are seven other temples to Ratri in the city, all with large, active congregations.