No, that's not a zen jail cell. That is a claustra, which let the light in, back when there was a roof above the slabs.

The central gallery, which was started by Amenophis III, is taller than the side aisles. The claustra were placed where the center met the sides, so the Sun could shine in during the morning and afternoon. The rest of the time, the place was lit up by light shining in from the tops of the obelisks.