Rooftop garden with 360-degree panoramic views and a hot tub
ZAO, YAMAGATA: Hoshino Resorts is pleased to announce the upcoming opening of KAI Zao on October 15, 2026—the premier onsen ryokan brand’s first property in Yamagata Prefecture and its 26th location overall. Situated amidst the quiet majesty of the Zao mountain range, the hotel invites travelers to uncover Yamagata's long-overlooked beauty through an innovative 14-sided tower designed to seamlessly integrate with the 360-degree natural landscape. Grounded in the region’s legendary thermal waters and rich, hidden heritage, KAI Zao introduces a modern wellness concept—"A Spiral Journey of Total Rejuvenation"—that pairs spatial design akin to fine art with an intimate discovery of local culture.
About Zao Onsen and KAI Zao
Located in Yamagata Prefecture—a region celebrated by discerning travelers for its unhurried pace and undiscovered cultural wealth—Zao Onsen offers a deep connection to Japan's natural and spiritual roots. The surrounding Zao mountain range is steeped in Sangaku Shinko (mountain worship), historically serving as a site of physical and spiritual purification for ascetic monks. Complementing this spiritual retreat are Zao’s famous strongly acidic hot springs, long revered for their therapeutic benefits and skin-rejuvenating properties. At the base of the mountains, Yamagata’s historic wealth from the benibana (safflower) trade fostered an elegant tradition of regional hospitality, cuisine, and artisanal craft. KAI Zao brings together these three elements—spiritual heritage, therapeutic waters, and vibrant local art—to introduce guests to the multi-layered charm of Yamagata. Through a curated sequence of hot spring bathing, mountain exploration, and ever-changing seasonal landscapes—from autumn foliage to a winter skiing haven—the property delivers a holistic wellness experience available throughout the entire year.
Feature 1: A 14-sided Architecture Embracing Nature from Every Angle
Set against a dramatic mountain backdrop, the property features an innovative 14-sided tower designed to elevate the guest journey. Moving sequentially from the ground-floor entrance up through the guest rooms, bathhouse, and top-floor wellness area, visitors experience shifting natural vistas that encourage relaxation. This creative spatial design—unprecedented for an onsen ryokan—architecturally tells the story of an ascent up a sacred mountain.
Exterior design
Feature 2: An Active Wellness Journey: From Acidic Hot Springs to the "Okama" in the Sky
Anchored in the concept of "A Spiral Journey of Total Rejuvenation," KAI Zao presents a structured wellness experience using Zao Onsen’s famous strongly acidic sulfur waters. To optimize the health benefits while preventing bath fatigue (yu-atari), the thermal baths are divided into three distinct concentrations: 0% Onsen for preparation and final rinsing, 50% Onsen to gently acclimate the skin, and 100% Onsen featuring pure, 100% free-flowing thermal spring water (kakenagashi). Following this step-by-step detoxifying bath, guests progress through saunas, hot-and-cold alternation therapy, and indoor air bathing before reaching the top-floor rooftop garden. The experience culminates in an outdoor hot tub designed in the likeness of Zao’s legendary "Okama" crater lake, offering full-body liberation under an expanse of 360-degree mountain skies.
Spring Quality: Acidic, sulfur, iron-containing, aluminum-containing sulfate and chloride hot spring
Feature 3: KAI Signature Room —"Crimson Modern Room"
The property's signature 14-sided architecture creates distinct trapezoidal guest rooms, each offering unique ceiling heights and directional views that showcase Yamagata’s dramatic landscape like framed artwork. Designed to immerse guests in regional culture, the interiors showcase master craftsmanship from local artisans, including woodwork by the renowned Tendo Mokko and handtufted rug tapestry by Yamagata Dantsu. Accent elements include benibana washi (safflower paper) lampshades that emit a gentle, warm light through embedded safflower petals, and "Flowers That Never Fade," an innovative artwork pairing ultra-thin natural wood with historic safflower dyeing techniques. 
Feature 4: Transforming the sophistication of safflower merchants into modern Shojin cuisine (monastic vegetarian cuisine): "Benibana Sansai Kaiseki," which nourishes the body and beautifully restores balance
Dinner is served in refined, semi-private dining spaces where pendant lights inspired by safflower motifs cast an ethereal glow. Celebrating Yamagata’s bountiful food culture, the "Benibana Sansai Kaiseki" inherits the sophisticated spirit of safflower merchants who entertained their most honored guests with the region's finest regional offerings, alongside the body-nourishing philosophy of shojin (monastic vegetarian) cuisine. Highlighting Yamagata's abundant mountain ingredients, the kaiseki course begins with the "Bejeweled Delicacies," an assortment of seasonal mountain delicacies served in striking vermilion-lacquered dishes. The centerpiece is the "Gassan Nabe," a regional hot pot combining fragrant Japanese parsley (seri), five types of wild mushrooms, and savory duck meat. Enhanced by a secret dashi element—locally harvested mitten crab (mokuzu-gani)—the broth delivers an unexpected depth of flavor where land and mountain umami harmoniously meet. Designed to nourish the body after a day of hot spring bathing, this dining experience exemplifies the authentic taste and restorative wellness of Yamagata. 
Feature 5: Detoxing Your Mind with a Haiku Writing Experience
As part of the brand's signature KAI Cultural Discovery program—a local cultural activity offered at every KAI property across Japan—KAI Zao presents a haiku writing experience that encourages guests to express their inner selves. The journey opens with warm safflower tea and an introduction to the region’s history. Afterward, with a mind relaxed from the thermal springs, guests compose a traditional 17-syllable haiku using elegant glass pens and seasonal inks. This quiet moment of reflection washes away everyday distractions, gently restoring and enriching the spirit. 
Property Overview
Property Name: Hoshino Resorts KAI Zao
Address: 903-2 Zao Onsen, Yamagata-shi, Yamagata 990-2301
Telephone: +81-50-3134-8092 (KAI Reservation Center)
Number of Rooms: 49 rooms
Rate: From 31,000 JPY~ per person per night (for 2 guests sharing 1 room, tax and service charge included, dinner and breakfast included)
Facilities: Public bath, post-bath lounge, sauna, cold plunge pool, indoor air bathing space, lounge, rooftop garden (equipped with jet bath), KAI Cultural Discovery Room, dining area, shop, ski drying room
Access: Approx. 40 minutes by car from JR Yamagata Station; approx. 45 minutes by car from Yamagata Airport
Opening Date: October 15, 2026
Project Specifications
Site Area: 6,320.03 m²
Building Area: 1,212.53 m²
Total Floor Area: 6,127.29 m²
Architectural Concept & Basic Design / Overall Design Supervision: Shuhei Kamiya + KAMIYA ARCHITECTS
Landscape Design: ORIZA Co., Ltd.
Detailed Design & Supervision: Asai Ken Architectural Research Inc.
Construction: Ichimura Koumuten Co., Ltd.
From Shuhei Kamiya / Architect & Creative Director
"We conceived an architecture that embodies the culture, climate, and local identity of Zao. Clued in by the landscape of the Okama crater, memories of mountain worship, and physical sensations as a hot spring destination, we built the entire property through repeated dialogues with many makers, including manufacturers and artisans around Zao. We hope this becomes a place where guests can encounter unique experiences peculiar to this land throughout all four seasons, not just in winter."
About the "Hoshino Resorts Tourism Activation Fund"
On October 30, 2020, Hoshino Resorts and Risa Partners, Inc. formed and operated a fund that invests in domestic accommodation facilities. Through the Hoshino Resorts Tourism Activation Fund, Hoshino Resorts and Risa Partners, Inc. invest in outstanding tourist destinations in Japan, aiming to contribute to the growth of Japan's tourism and lodging industries. KAI Zao marks the 3rd project under this fund, following KAI Okuhida in Okuhida Onsen-go, Gifu Prefecture, and KAI Akiu in Akiu Onsen, Miyagi Prefecture.
About KAI Brand
Onsen Ryokan loved by local and overseas travelers
KAI is a leading brand of onsen ryokan (hot spring inns) with an expansive nationwide presence that invites guests to explore Japan’s hidden regional beauty. Each establishment offers a contemporary take on the traditional Japanese inn, balancing local heritage with modern comforts. KAI invites one to discover the multifaceted aspects of Japan through natural hot springs, exploration of local arts and entertainment, and regional dining using local and seasonal flavors. While deeply honoring these traditions, KAI elevates the experience with bold innovations—from introducing tattoo-friendly bathing to offering diverse vegetarian and Western culinary options.
About Hoshino Resorts
Hoshino Resorts was first established as a Japanese inn/ryokan in 1914 in Karuizawa in Nagano Prefecture before it began the operation of other resorts in Japan. Today, it has evolved into a highly influential hotel management company and is run by 4th-generation family member Yoshiharu Hoshino. Providing a unique experience focused on the local charms of each destination and a high level of omotenashi, Japanese-style hospitality, the company has expanded rapidly out of Karuizawa since 2001 and now operates more than 70 accommodations both in and outside Japan with one of the following categories: luxury hotel brand "HOSHINOYA", hot spring ryokan brand "KAI", countryside resort hotel brand "RISONARE", city tourism hotel brand "OMO", free-spirited hotel brand "BEB",mountain hotel brand "LUCY" or other unique lodgings.
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