The Church of Saint Peter

These are walls of the original church, with the new, glass floored church built over it on stilts.
From Wikipedia
The Octagonal Church
The 5th-century church consists of a central octagon with eight pillars, an exterior octagon with thresholds still in situ, and a gallery or portico that leads both into the interior of the church as well as into a complex of associated buildings to the East, a linkage achieved via a short passageway. Later, this passage was blocked and an apse with a pool for baptism was constructed in the middle of the east wall. From this wall ascended two stairs on either side of the baptistry, and the excess water from the rite would have escaped along this path. The Byzantines, upon constructing the new church, placed the central octagon directly on top of the walls of St. Peter's house with the aim of preserving its exact location, although none of the original house was visible any longer, as the walls had been torn down and the floor covered in mosaics.

In the portico, the pattern of the mosaic was purely geometric, with four rows of contiguous circles and small crosses. In the zone of the external octagon, the mosaics represented plants and animals in a style similar to that found in the Basilica of the Feeding of the Five Thousand, in Taghba. In the central octagon, the mosaic was composed of a strip of calcified flowers, of a field of schools of fish with small flowers, and of a great circle with a peacock in the center.