Flânons

Karuizawa · Japan · To stay

NOT A HOTEL - Base L/M/S

Location & practical

A House That Fits

  • A-frame architecture beneath Mount Asama.
  • Private saunas and forest-facing terraces.
  • Three sizes, two palettes, complete privacy.
  • €1,000–3,000 / night
  • 11 rooms
  • Kitakaruizawa / Mount Asama foothills, Tsumagoi, Gunma Prefecture

When NOT A HOTEL approached Yosuke Aizawa, he assumed they wanted uniforms. A reasonable misunderstanding: the founder of fashion label White Mountaineering had spent his career designing clothes, rather than houses. Instead, he was asked to imagine a retreat in the Japanese mountains. His answer came in three sizes, S, M and L, and two colours, NATURAL and BLACK. A home, he reckoned, ought to fit its occupants as comfortably as a favourite jacket.

Some 35 minutes from Karuizawa station, the houses stand among towering trees and enormous volcanic rocks at the foot of Mount Asama. The forest had been largely undisturbed for decades, and looks it. Steep triangular roofs give the cabins a familiar silhouette, while expansive glazing, warm timber and beautifully considered details make them thoroughly contemporary. Every house has a private sauna and terraces opening onto the forest, where summers are pleasantly cool, autumn brings spectacular colour and winters deliver proper snow.

The smallest, BASE S, is an intimate hideaway for two, complete with a desk overlooking the trees. BASE M accommodates four, with generous space for cooking, dining and evenings around the fire. BASE L welcomes up to eight, beneath a dramatic six metre ceiling, with a fireplace, spacious outdoor living areas and a natural hot spring bath carved from stone. Aizawa personally travelled to Manazuru to select the rocks for the baths. He also insisted on real outdoor fires, sensibly leaving their preparation and cleaning to the hospitality team.

Days here can be as active or uneventful as you please. Explore the surrounding highlands, discover the local hot springs or visit nearby ski slopes in winter. Alternatively, prepare a leisurely breakfast, settle down with a book or spend an afternoon moving between the sauna and the terrace. Cooking together is part of the pleasure, with well equipped kitchens and plenty of space to enjoy a long dinner.

For all their architectural ambition, these houses feel wonderfully domestic. There is little ceremony, plenty of privacy and a genuine appreciation for the simple pleasures of mountain living. The sort of place where a weekend's most pressing decision might be whether to light the fire before or after another bath.

  • Restaurant

Rooms.

The Flânons choice

Which room would we choose?

BASE L for families or groups who want the full mountain-house experience, including the private rock onsen; BASE M for four guests who value space to cook and gather; BASE S for two people wanting a quiet retreat with a forest-facing desk and solo sauna.

All 3 room types

BASE S

2 adults

46.21 m²

Forest view · Private sauna · Terrace · Work desk · Full kitchen · Outdoor fireplace · Stairs

One bedroom; approximately 28.62 m² of additional outdoor space (74.83 m² total). Especially good for a couple or solo retreat and a little work overlooking the trees. No private natural hot spring.

BASE M

4 adults

91.99 m²

Forest view · Private sauna · Terrace · Full kitchen · Outdoor fireplace · Two bedrooms · Stairs

Two bedrooms, one bathroom and 57.32 m² of outdoor space (149.31 m² total). Ideal for four; dedicated pet-friendly BASE M-2 is available subject to house rules. No private natural hot spring.

BASE L

Up to 8 guests

158.65 m²

Forest view · Private sauna · Natural hot spring · Outdoor living · Fireplace · Terrace · Full kitchen · Children playroom · Stairs

Three-bedroom configuration in the official sales listing, including a children’s playroom in the accommodation guide. Spacious living and dining, 156.55 m² of outdoor space (315.20 m² in the original configuration), 6.3 m ceiling and private rock onsen. Standard occupancy is four; for up to eight, confirm adult sleeping arrangements and extra-bed costs. Dog-friendly L-2 is documented; confirm status of newer L-5.

BASE S sleeps up to two (46.21 m² indoors), BASE M up to four (91.99 m²), and BASE L up to eight (158.65 m² in the original model). Although BASE L is marketed as three bedrooms, the accommodation guide describes two conventional bedrooms plus a children’s playroom, with standard occupancy four and maximum eight. Confirm bed arrangements and any extra-bed costs for adults before booking.

Good to know.

Location
Japan, 〒377-1512 Gunma, Agatsuma District, Tsumagoi, Ōmae, 字細原2286
Open map & directions
Contact
notahotel.com
Check-in & check-out
Check-in from 15:00, until 22:00, check-out by 11:00
Parking
Dedicated guest spaces: two per BASE S or M; three at BASE L-1/L-2, and four at BASE L-3/L-4/L-5, according to the official guest parking guide.
EV charging
The official guest guide lists EV charging arrangements at Kitakaruizawa, with model-specific compatibility details. BASE users may need their own adapter. Confirm connector, power, access and reservation requirements before arriving.
Getting around
Take the Hokuriku Shinkansen to Karuizawa Station, then travel approximately 23 km (35 minutes) by pre-arranged taxi or car. There is no convenient direct train or bus to the forest houses. NOT A HOTEL offers advance-bookable Tesla car sharing from Karuizawa Station; confirm eligibility and charges.
Arriving
Located on forested grounds in Tsumagoi, Gunma, rather than central Karuizawa. Arrange the final transfer in advance. Check-in and door access use the NOT A HOTEL app/website on a smartphone; house controls use an in-house iPad. Allow for winter driving conditions, and follow the property wildlife guidance, especially around dusk and dawn.
Pets
Dogs are accepted only in designated houses: BASE M-2 and BASE L-2 appear in the current guest help centre; a newer sales comparison also lists BASE L-5. Check the precise house before booking. Dogs are not permitted in bedrooms. Other pets are not accepted; dog-run access and house rules apply.
Accessibility
The houses have two-storey layouts and stairs; step-free access and adapted bathrooms have not been confirmed. Guests with mobility needs should request the exact floor plan and access information before booking.
Travelling with children
Children of all ages may stay. BASE L is particularly suitable for families, with a children’s playroom. Child amenities and meals may be requested; children aged 13 and over are treated as adults for meal orders. Confirm extra bedding for larger groups.

Worth knowing

  • NOT A HOTEL operates primarily through fractional ownership, and availability to non-owners varies by residence. Choosing your favourite villa is therefore only half the exercise. Securing a stay may require a little more planning.
  • Nightly budget for BASE S, M and L: €1,000–€3,000 per entire villa is an INDICATIVE EDITORIAL PLANNING BAND, not a verified published minimum or maximum, a live quote, or a guarantee of public availability. The only independently reported rate benchmark located was approximately ¥253,300 per night averaged across Kitakaruizawa plans in June 2026 (approximately €1,442 at the ECB rate of €1 = ¥175.68 on 30 October 2026). Request a live price for the specific BASE house and dates; the much larger figures on the developer website are fractional-ownership purchase prices, not nightly accommodation rates.
  • For non-owners, reservations are possible at selected NOT A HOTEL properties through the general-customer Reserve function, but the BASE villas may not be offered on every date. The Ikyu public listing currently shows no rooms without changing dates. Confirm public access and house type before promising a stay.
  • The outdoor natural hot spring bath belongs to BASE L; S and M have private saunas but should not be advertised as having a private onsen. There is no communal swimming pool listed for BASE.
  • Dogs are allowed only in specific BASE M and L houses, never automatically across the collection. Check the exact house designation and current pet rules.
  • The property is in genuine forest habitat. Official guidance mentions seasonal wildlife, including bears, as well as electric fencing, bells and repellent; avoid going out alone very early or late in the active season.
  • The much-publicised children’s park and gym are planned additions rather than facilities to promise for an immediate stay.
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