The Trinity Cathedral is the oldest stone building preserved in Poshekhonye. Its main part is a massive two-light square-like structure topped with a high five-domed roof. To the east, it has a three-apsidal altar section, and to the west, a small rectangular refectory. The design of the cathedral resembles the Cathedral of the Epiphany of the Ostrovsky Monastery from 1702. Thick walls and two powerful square pilasters support a system of spring arches and cross vaults. The central dome has a light drum, while the side domes are blind. The exterior of the cathedral is simple: windows on the northern and southern walls are arranged in groups of three in the upper tier and one on each side of the portal in the lower tier. Currently, the lower windows and portals are partially lost. A cornice with teeth serves as the base for five semi-circular kokoshniks on each facade. On the western wall, two small cross-shaped windows, symmetrical in placement, appeared in the second half of the 18th century. At the same time, the corners of the square were decorated with rustication.

The interior decoration of the cathedral has not survived; only small fragments of 18th-century wall paintings remain. To the northwest of the cathedral rises a four-tiered bell tower built in the second half of the 19th century, reminiscent of the lost bell towers of Yaroslavl. Three massive cubic volumes serve as the base for a rotunda with high arches topped with a dome. This composition is characteristic of the projects of Academician K.A. Ton, whose influence is noticeable in provincial architecture of the 19th century. The decoration of the bell tower is also done in this style: the first tier is adorned with a frieze of kokoshniks with a round window in the center. The arched openings of the lower tiers are framed by faceted half-columns with an entablature and pointed archivolts. The walls of the upper tier are decorated with Tuscan pilasters. To the north of the cathedral was the now-lost warm church of the Nativity of Christ, which was part of the cathedral complex.