If you've toured Palenque, it's quite likely that you've climbed these stairs and walked right through the middle of Temple XXI. The roof fell in a long time ago, and all that remains are low walls demarcating a central passageway and two side rooms. In the center of the floor you might have noticed a square hole where looters removed a cache in Precolumbian times. It's even more likely that you came this way on your return from visiting Temple XIX and its replicas of new discoveries, because the rear approach is closer to ground level.