That thing we call "sky" appears to be the earth´s “roof”. A huge self-supporting dome, without pillars. This primary interpretation is echoed in the etymology of the word, which refers to the notion of cover. It has a persistent, ever-present character, which means, it is a sort of endless roof, whose only limit is the line of the horizon. A limit that also re-configures itself, endlessly. We may travel a few or a thousand miles, and, strangely enough, the sky is still there, “up”, hovering far above our heads. What seems to change is just its appearance: luminous during the day, dark at night, veiled by passing clouds, dyed in beautiful colours at dawns and sunsets. Somehow, it has no age. Unlike the rest of the entities that surround us, which reflect the passage of time in the form of aging and decay, the sky is timeless. In this sense, it is the closest form of manifestation of what we may designate as "the Absolute". This is a shared attribute with all those things that are regarded by us as heavenly: the sun, the moon, the stars, and divine beings of all sorts. Technology has allowed us to enter the sky´s realm, thus being not anymore the privilege of birds and creatures provided of wings and feathers by nature. But, somehow, it remains an alien medium for humans, an irreducible form of otherness, just like water and the ocean´s unfathomable depths. The ancient myth of Icarus makes the point. Will we ever make of the sky a ground for permanent inhabitation, turning this roof into a soil for digging foundations?