The architectural ensemble of the Shartomsky Monastery was mainly formed in the second half of the 17th century and the first half of the 19th century. The central element of this ensemble is the Nicholas Cathedral, which is considered the oldest building of the monastery. In a petition addressed to Alexei Mikhailovich, Archimandrite Joasaph describes how after the fire of 1649, the monastery's elder, who was collecting money for the monastery, was killed and robbed by Ivan Akhmetev. This indicates that funds for the construction of the monastery in the mid-17th century mainly came from the peasants of the monastery lands. Since there was no response from the tsar, the money was collected again, and already in 1651, a new stone cathedral was consecrated by Archbishop Serapion of Suzdal and Torzhok. However, it cannot be said with certainty that the construction of the cathedral was completed in that year, as the date is taken from a cross that may have been consecrated earlier or during the construction of the church. Thus, although 1651 is considered the date of foundation, it is possible that the monastery was only completed by the second half of the 1650s.

The Nicholas Cathedral, along with the monastery, experienced the decline of the late 18th century when all possessions were lost, the flourishing of the second half of the 19th century, and the devastation of the 20th century.

The cathedral is a four-pillar church with four green onion domes and one golden dome. The roof has likely been gabled since its construction, but overall the architecture of the cathedral remains conservative. The foundation is made of boulders, granite, and partially of white stone. The exterior walls are covered with whitewash over brick. The external division of the walls into sections continues inside the cathedral. The central dome is shifted further east than usual, causing the columns to also be shifted to the east. The western section is the widest, the middle is narrower, and the eastern is the narrowest, built on the principle of the golden ratio. The three-apse altar is twice as low as the square of the temple, giving it a stern appearance. The cathedral's windows are long and narrow, arranged in two tiers. The windows of the lower tier have frames with pointed finishes, while the windows of the second tier are unframed. The middle window, the altar window, is the only one with a rounded top, and the southern apse protrudes slightly more than the northern.

Inside the cathedral, the walls are plastered, and remnants of tempera painting from the early 19th century have survived. By the time the monastery was transferred to the Church, the interior decoration of the cathedral had been almost completely destroyed. On the internal walls, vaults, and edges of the pilasters, plaster with remnants of frescoes has survived in places. Three perspective portals consist of alternating quarters and semi-ovals. The northern portal is decorated with carved white stone elements reminiscent of the portals of Vladimir-Suzdal architecture of the 12th-13th centuries. The base is decorated with a decorative strip. The temple houses ancient icons. To the left of the choir are the Tikhvin and Shuya-Smolensk icons of the Mother of God, and to the right is the not-made-by-hand image of the Savior with expressive writing. By their size, it can be assumed that these icons once belonged to the iconostasis of another local church.