Il Duomo di San Giovanni - or Church of Saint John - adjoins the Royal Palace of Turin (Palazzo Reale) by way of the Chapel of the Holy Shroud, which is found in the west wing of the palace. The church itself sits upon the site where three previous churches stood. These three, demolished in 1490, were built in the 500s on top of the former site of the Roman theater. The current church was completed in 1498.
Visitors primarily come to the Church of Saint John in order to view or at least be near the Shroud of Turin (as it is not usually on display). The church's adornments are typical of the period, though the campanile (bell tower), completed in 1470, is of a slightly older style.
Besides the Holy Shroud and the church, the adjacent Palazzo Reale is worth touring as well; in 1946, it was made into a museum dedicated to the House of Savoy, and it is decorated (somewhat curiously) with priceless tapestries and Chinese and Japanese vases. Its armory is of particular interest, as it holds a vast array of armaments, including then-contemporary arms from the 16th and 17th centuries.
