The Kiev Psalter aka the Spiridon Psalter, is one of the most famous East Slavic illuminated manuscripts, containing over 300 miniatures. It was written and scribed in 1397 by Archdeacon Spiridon in Kiev. which followed a Byzantine style from an 11th century Psalter. The weighty and elegant script and large size of the page adds to the impressiveness of the book. Many of the miniatures illustrate passages from a psalm, with thin red lines drawn between miniature and text to indicate the indented passage. Sometimes the meaning of the illustration is explained in long notes in the same thin red draft (apparently original).
Each leaf is about 30 x 24.5 cm, larger than a typical Byzantine psalter. The Psalter passed through the hands of numerous Lithuanian nobles before being sold to the Russian Count Sergey Sheremetev in the mid-19th century. Courtesy of the Count, its first printed edition was prepared by Nikodim Kondakov and Fyodor Buslaev. It became an item belonging to the Sheremetev Libary, which in 1932, merged into the Russian National Library in St Petersburg. Whether it is still on display, I do not know.
If it is still available to see, make an effort and do not alter; do not falter; or halter your course, in your effort to see the Kiev Psalter.