Alberto Kalach’s architecture exists in an extraordinary world, a world at once mechanistic and primordial. This is a world fascinated by structure and the use of reason yet simultaneously open to nature and the vagaries of sensory pleasure. Indeed, it may be that Kalach’s architecture creates such a world, inventing architectural form that allows the sky and rain, earth minerals and chlorophyll to co-exist in light and in shade. Kalach’s most recent building, Torre 41, is a small commercial tower of independent character at 41 Constituyentes Avenue in Mexico City. This new tower is not about facadism or glitz or the homogenous ennui of international capital. Rather, it rethinks the essential components of a tower: vertical structure, horizontal structure, services, the building envelope, the building’s connection with the ground, and the building’s connection with the sky. It provokes many key architectural questions. Years ago, Aldo van Eyck proposed the cigarette machine test. Would the introduction of a vending apparatus destroy the integrity of a specific architectural space? Exploring the interiors of Torre 41, it is apparent that this daring structure is more than capable of accommodating the accumulation of artefacts. It is in fact both robust and beautiful. Kalach’s own studio, on the first of seven office floors, is already packed with desks and bookshelves and architectural models. These spaces can fill up without losing direct visual contact with the outside world through floor-to-ceiling membranes of glass. Is there a big idea? The main design move at Torre 41 is to sling taut slabs between non-identical party walls, structural blades to the east and the west. The result is work areas free of columns and with exposed ceilings. Office suites as decks or bridges in the sky. This, and the liberation of almost the entire ground area for communal use, may recall Foster’s strategy for the far larger Hong Kong Shanghai Bank now three decades ago. Yet the aesthetic of Torre 41 is to consider architecture less like product design and more as visceral experience. Are there remarkable details? Throughout the tower, there is an ingenious resolution of practical needs, with many components tucked within the triangulated volume of the westerly party wall. These clever mechanical details share some affinity with Pierre Chareau and Bernard Bijvoet’s Maison de Verre in interwar Paris, a house and doctor’s office that is clinical yet full of intimate charm. And then, as so frequently in Kalach’s architecture, both domestic and institutional, there is the copious planting with nature almost superseding the built fabric. The site, it turns out, is not orthogonal. Constituyentes is a busy thoroughfare between a dense urban neighborhood (Barragán’s Casa Gilardi, with its famous indoor swimming pool, is close by) and Chapultepec Park with its mature trees and such national monuments as the iconic Museum of Anthropology and Mexico’s presidential palace. The orthogonal grid of the neighborhood meets the Constituyentes axis at almost a 45-degree angle. Does the building rationalize its grids and boundaries? Front and back elevations are parallel to Constituyentes and to one another, but are sharply skewed vis-à-vis party walls and the rear of the lot. Kalach capitalizes on these confines, exposing for instance the crisscross ribs of the office ceilings. Indeed, the architect literally highlights this harlequinade pattern - an interpolation of the site geometries - through soft illumination. A seminal test for any freestanding tower is to examine its relationship to the ground. The site on Constituyentes is screened from the relentless traffic outside. The tall glass wall of the tower and exposed steel struts propping up the lowest floor plate are visible above a high timber palisade. Several panels in this gently weathered palisade open, seamlessly, into a sheltered garden. One path leads to a reception desk of cantilevered lumber beneath a delicate glass canopy. A second is for cars. The ground surfaces crack and tilt, like tectonic plates found in nature, allowing pedestrians to ascend as automobiles descend into a basement garage where an automated stacking system occupies the rear of the site. The character of this interplay of strata and the infrastructure of the building is both pragmatic and telluric. Natural light seeps into this compact undercroft in multiple ways. An array of glass disks in the garden above admits a pale light; these incisions in the raw concrete slab are unexpectedly lined in pale metallic paint (a nod, perhaps, to Le Corbusier at La Tourette). The paraphernalia of doors and equipment is unabashedly on view. Tucked to one side, several little spaces for services are an essay in spatial juggling and perimeter management. These lower levels evoke a primal sense of inhabiting the earth’s crust. The garden above, sloping up from Constituyentes, also seems feral, albeit open to the light and air. It may even suggest an intimate jungle with its ludic planting of bamboo, fern, small palm, floripondio and indigenous tepozan (beloved by butterflies and bees) interspersed with volcanic rocks. Kalach introduces slivers of mirror in the garden wall and in the elevator cab. The ground plane is lined in fragmented strips of stone. A small polygonal fountain of weathered steel provides further sensory stimulation. An open metal staircase drops down, trapeze-like, from the soffit of the tower above. Up there, in the office suites that are the commercial raison d’être of the project, the visitor is inevitably impressed by the light and by the panoramic views of Chapultepec Park. Vertical panels in the extensive glass façades open to provide comfortable cross-ventilation. On occasion, the glazed elevations cant outwards in plan, allowing for further tiny spaces like the miniature balconies on the garden façade (a smoker’s delight). Vertical incisions in the poured concrete walls to either side of the tower admit air and tantalizing glimpses of traffic on Constituyentes. All seven office floors share access to the richly planted roof terrace, screened against the sky by a dramatic steel trellis. There is again something primal in this raw partial-space, a simultaneous sense of elementary enclosure and, conversely, exposure to the park, to the metropolis and to the sky. Torre 41 passes many key architectural tests, including the provision of shelter in both the physical and psychological meaning of shelter. It is both human-scaled and monumental.