Owarimonogatari English vol 1

From the best selling novel series comes the latest book of the final season of the Monogatari Series.

During his third year in high school, Koyomi Araragi is introduced to a transfer student named Ougi Oshino Ougi tells Koyomi that there is something odd about Naoestu High School… a secret room on thats not on the map.
What will Koyomi and Ougi find in this hidden room?