The Klementinum is a complex of historic buildings in Prague dating back to 1232, consisting not only of a grand central library and an observatory tower that played host to some of Europe’s greatest scientists and intellectuals over the past centuries, but also of two cathedrals and a beautiful mirror chapel. If you’re strolling around the Old Town, it’s impossible to miss these churches, they’re right on the route between the Old Town Square and Charles bridge, a well-beaten tourist path filled with merchants and hawkers looking to make a quick buck. Nonetheless, this doesn’t detract at all from these Cathedrals, both of which are beautiful examples of Baroque architecture. St. Salvator is the older of the two, built by Jesuits in the 16th and 17th centuries, with St. Clement following soon after, and both feature high halls and excellent acoustics, lending themselves naturally to classical and church organ concerts. St. Salvator and the Mirror Chapel both feature not one, but two organs; the Mirror Chapel in particular was favored by one Wolfgang Amadeus Mozart, who would play there on his visits to Prague. Concerts do tend to be on the more expensive side, however, and cheaper ones can be had a little further away from the Old Town or in Mala Strana, if you want to visit, do keep in mind that both can be visited for free during non-concert hours.