The central image in the cathedral’s iconostasis—the Holy Trinity icon painted by Andrei Rublev. One of the most famous Russian icons, it was created “in praise of St. Sergius”. The original is carefully preserved in the hall of Old Russian painting of the Tretyakov Gallery, in a special glass case with controlled humidity and temperature. In Trinity Cathedral you can see a copy of the icon to the right of the royal doors in the first (lowest) tier of the iconostasis.