When entering the mandapa you will see a narrow stairway on the left (closed to visitors), which leads to the top of the mandapa. On the ceiling of this stairway there used to be slate slabs decorated with Jataka tales (previous lives of the Buddha). They are not anymore in place and some are kept (not for the public) at the Ramkhamhaeng National Museum in Sukhothai. The same museum displays quite a few replicas of the decorations.