Two factors determined the paired buildings' angular façades: the site location among built up small streets and blind alleys and the zoning regulations. The structural ensemble that emerges is formed from two skins: an interior core in tune with traditional architectural construction found regionally and a steel exoskeleton wrapping the interior core. The exoskeleton has a thin, light cable structure that serves as support for vines, vertical "green" walls and landscaping. This outer skin expertly screens the interior core and gives a unified identity to both buildings as a whole, while ensuring that each building retains its own character based on orientation and growth patterns. This in effect yields three distinct layers: the interior core, the metallic skin, and the dynamic bands of greenery that slink over the building, changing over time and through the seasons. The result at a distance is a brutalist monolith that emerges abstractly from the surrounding low rise buildings. At closer range the chiseled monolith reveals its layers and the depth of its angled planes.

Not unlike the buildings' namesake, the mythological twins Castor and Pollux, the two buildings are born from the same process, yet have unique characteristics based on their location and relationship. Castor rises up between two buildings on the historic street wall of Rue du Liban and is thus restrained until it tilts towards the light of the alleyway creating outdoor rooms with green walls. Pollux, (the immortal twin) on the other hand, is less constrained by its surroundings and twists to face both Castor and a neighboring church.

The two residential structures are split into two 140 m² apartments per floor on the initial seven floors before breaking out into full floor, three-bedroom apartments ranging from 200 to 280 m², ending with a duplex penthouse of 350 m2. While residents of both buildings access private garages from the blind alley facing "Centrale", visitors to Castor access from Rue du Liban – otherwise known as Zaroub El Haramyeh. The ground floor of both buildings has been given over to retail space.