Original featureA Luxurious Spa by Liaigre Completes Hôtel Costes in ParisDesign Milk · 6 October 2026 →

Materiality and the Monolithic Palette

The subterranean wellness space relies on a tightly edited palette of natural materials. Travertine stone dominates the architectural surfaces, chosen for its tactile warmth and subtle veining, which softens the cavernous nature of a basement environment. Smoked oak introduces a contrasting deep, organic grain, grounding the voluminous chambers with artisanal cabinetwork and wall paneling that feels both contemporary and rooted in traditional French joinery.

Liaigre’s approach avoids fleeting decorative trends in favour of enduring textures. The combination of porous stone and dark wood creates a subdued acoustic and visual environment, establishing a sense of retreat from the urban density of the 1st arrondissement above. This disciplined material selection ensures the interior ages gracefully, maintaining its integrity through heavy commercial use.

Lighting as Spatial Architecture

Without access to natural daylight, the lighting design acts as the primary structural element. Subdued, immersive illumination washes down the travertine walls, highlighting the stone’s natural texture while eliminating harsh shadows. Low-level fixtures and concealed perimeter lighting emphasize the horizontal lines of the architecture, particularly along the length of the 20-metre, or 65-foot, pool.

This technique of indirect illumination can be translated to residential interiors, particularly in basement conversions or windowless bathrooms. By concealing light sources behind architectural reveals, designers can manipulate the perceived volume of a space, trading bright, flat illumination for atmospheric depth and shadow.

Proportion and Scale in Subterranean Spaces

Designing below ground presents distinct challenges regarding ceiling height and spatial confinement. The Hôtel Costes spa counters this by prioritizing long, uninterrupted sightlines and monumental proportions where possible. The 65-foot pool acts as a central axis, drawing the eye through the sequence of treatment rooms and relaxation areas.

For property owners undertaking subterranean expansions, the lesson lies in restraint. Rather than subdividing tight underground footprints into multiple small rooms, maintaining open sightlines and incorporating single, well-scaled elements—such as a continuous stone basin or a monolithic plunge pool—preserves a sense of architectural generosity.

Related reads

• Inside Liaigre’s Moody New Spa at Hôtel Costes (Design Milk, 6 Oct 2026)

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