Ακάλυπτος (akalyptos means uncovered in greek) is the mandatory empty space in the back side of polykatikia and it is what remains of the land plot when the permitted building coverage ratio is fully exploited and built. Its ultimate quality is exactly that it is uncovered, it exists due to a mere obligation to the building code and is often under-used, neglected, covered by cement and some sporadic vegetation, separated with blind walls from the adjacent akalyptos. Bringing down the walls between the akalyptos of each polykatikia around a building block in order to create a continuous green space in the interior of the block is a recurrent architectural fantasy of low-cost tactical urbanism for the remediation of Athens. Though technically a simple idea it remained utopian, given the difficulty of negotiations and agreements between all the owners of a building block.
With the introduction of polykatikia, back in 30s, the building coverage ratio was not yet regulated adequately by the law and it was up to each construction to find the ideal analogy, thus ending up with coverage of 80-90% or even 100% of the land plot. The 1955 law set the limit to 70% for the center of Athens, where it is till now, still quite high combined with the high floor area ratio which permits big heights in narrow plots. With the same law all the interior courtyards where abolished and fotagogos, the light well in the mass of the building to bring light in the auxiliary spaces, was limited to 1,20*1.20. So akalyptos remained the only potentially open-air, common-use space of polykatikia beyond the circulation spaces.