The Assumption Cathedral, built by order of Tsar Ivan the Terrible, was constructed from 1559 to 1585. Architecturally, it closely resembles the cathedral of the same name in the Moscow Kremlin, which served as its model, but it surpasses it in size. This is the largest church of the Trinity Monastery, yet its grandeur does not overshadow the older and smaller buildings of the monastery. The Assumption Cathedral borders the cathedral square on the eastern side.

The frescoes adorning the walls, pillars, and vaults of the cathedral were created in 1684 by a group of Yaroslavl and Trinity icon painters under the guidance of master Dmitry Grigoriev. The interior of the cathedral is complemented by a huge five-tiered carved iconostasis from the early 18th century with icons from the 17th century and two magnificent bronze chandeliers made in the Armory Chamber in the 17th century.

The main relics of the cathedral are the relics of St. Innocent, Metropolitan of Moscow, and St. Maximus the Greek. They are open for veneration during the warm season when the Assumption Cathedral becomes the main church for the monastery's services.

The Trinity Cathedral, the main cathedral of the monastery and the oldest of the surviving structures of the Trinity Monastery, was built in 1422 by St. Nikon in honor of the monastery's founder, St. Sergius of Radonezh. The relics of St. Sergius rest in a silver reliquary, the main shrine of the monastery.

The white-stone Trinity Cathedral is one of the key monuments of early Moscow architecture. Its construction marked the beginning of the formation of the unique architectural ensemble of the monastery. Unfortunately, the oldest frescoes of the interior walls, created between 1425 and 1427 by icon painters Andrei Rublev and Daniil Cherny, have not survived. The current frescoes, created in 1635, reproduce the ancient iconography. The main artistic treasure of the Trinity Cathedral is its five-tiered iconostasis, most of whose icons were created in the first third of the 15th century by Andrei Rublev and masters from his circle.