Local studio Heliotrope Architects has designed an upscale Italian eatery in downtown Seattle with clean lines, various tones of wood and a secret room tucked behind a one-way mirror.

Cortina is located at the base of Two Union Square, a prominent office tower in downtown Seattle. The restaurant's north-facing storefront, which stretches 100 feet (30metres), has large windows that usher in natural light while giving passers-by a glimpse of the interior.

Built with an L-shaped layout, the 7,000-square-foot (650-square-metre) restaurant has three distinct zones. The foyer and bar are situated in one leg, while booth-style seating and a secret dining room occupy the other. A lounge was placed at the corner, where the two legs meet.

Designed by local studio Heliotrope Architects, the restaurant is intended to have a calm and sophisticated atmosphere. All rooms have a highly disciplined appearance, with lines that are "crisp and clean".

"The architecture exploits the very long rooms by using a repetition of form and fixture to establish a rhythm to the design akin to a musical beat," said the studio.

The team used neutral colours and earthy materials, including various types of wood. White-panelled walls are paired with red oak ceilings. Underfoot, wide-plank flooring is made of white oak – a material used for decor as well.

"Detailing is simple but executed at a very high standard, focusing on the inherent beauty of the natural materials and subtle shifts of light and shadow across the finishes," said the studio.

The secret dining room is accessed via a door that looks like a panelled wall. The covert space features dark walnut panelling and seating for up to to 40 guests. One side of the room is lined with a one-way mirror, enabling guests to peer out while blocking anyone from seeing inside.

The 63-foot (19-metre) bar – among the longest in the city – is faced with granite and topped with wood. Suspended overhead is a long row of black, cylindrical pendants by XAL Lighting. The skinny fixtures send light downward, illuminating diners' cocktails and meals.

The dining areas feature pale wooden chairs by the Spanish furniture brand Andreu World, and disc-shaped sconces by Rich Brilliant Willing. Banquettes and booths are wrapped in smooth, brown leather.

In the lounge, banquettes are paired with small black tables and low clamshell chairs in a grey hue. Floating above is a chandelier made of colourful, blown-glass orbs that add a dash of exuberance to an otherwise subdued space.

Founded in 1999, Heliotrope Architects has completed a range of projects, from commercial projects in urban locales to modern dwellings in the forest. Other projects by the firm include a cedar-clad home that features a double-height art studio, a Japanese garden and a wooden soaking tub.

Photography is by Haris Kenjar.