Reisen Mamanenoyu観世音霊泉 ま々根乃湯

Reisen Mamanenoyu is the opposite of the municipal day-use model. Where Kogome no Yu is a town facility with gendered wings and a 2F rest room, Mamanenoyu is a single semi-basement bath underneath a small ryokan in Yugawara's oldest onsen lane, operated continuously for more than a hundred years and currently kept by the fourth-generation female proprietor. There is no website. There is no signage in English. The official name carved on the entrance is 々 - a Kannon-dedicated (sacred spring), which tells you almost everything you need to know about the register this place operates in.

The water is the reason it exists. Lot 22 - a sodium-calcium chloride-sulfate spring, weakly alkaline, source temperature around 82.8°C, pH 8.4, the same spring type family that defines Yugawara - but delivered with no dilution, no recirculation, no chlorine, no reheating. The operator's claim is 100% source-fed hot-spring water with the source immediately adjacent to the bath, and in 2025 that claim earned a third-party Pure Onsen certification - a meaningful attestation in a landscape where 'kakenagashi' is marketed loosely. Reviewers with broad onsen experience describe the mineral density as 'among the strongest they have personally encountered.' There are no chlorine-smell complaints in any source we read.

The bath itself is austere: one indoor tub of modest size in the center of a plain washing room, no open-air bath, no sauna, no cold bath, no reservable private, no bedrock bath. (Niftyonsen's structured record marks open-air bath ○; every first-person account we could find describes only the interior bath, and we trust the first-person corpus.) Water temperature is reported across visits in the 43-46°C range - genuinely hot, and explicitly not user-adjustable. water added (adding water to cool the bath) is prohibited; the protocol is to get in, get out, and cycle. One recent reviewer described being 'so intensely hot that movement became impossible' - treat that as documentation, not as hyperbole.

The etiquette is enforced, and enforcement is part of the experience. Every bather washes thoroughly with soap at the washing area before entering - this is not optional and regular patrons will correct a first-timer. No towels in the water. No casual heat-management behavior. The operator's posted purpose is therapeutic bathing for burns, cuts, and post-surgical recovery, and the stated policy is therapeutic guests only; day-use is permitted but not promoted, and a drop-in who reads as a casual tourist can be turned away. One reviewer was invited in only after a chance street meeting with the female proprietor. Payment, for women, happens through a curtain opening - this is how the building has always worked and it is not going to be modernized for you.

The economics are almost implausible. Day-use admission is ¥300 flat - we treat this as a flat fee based on multiple recent first-person reports, while noting that one structured-data source (Niftyonsen) lists it as ¥300 per hour; this is an old field we believe is stale. Children ¥100, toddlers ¥50. Soap is ¥100 on-site. The facility also sells a named commemorative towel for ¥400, which is a minor cult item - the printing is reportedly faint when new and darkens visibly after use, a small piece of Mamanenoyu folklore worth picking up if you are there. Parking is six free spaces (onsenzanmai) - Surugabank's write-up suggests ¥100/hour may apply, which we note as a contradiction. Hours are 8:00-20:00, closed the 10th, 20th, and 30th of every month. Phone 0465-62-2206 to confirm for a dated trip.

Mamanenoyu's place in the Yugawara onsen mix: it is the 'serious' bath - the one you visit when the water is the reason, when you are willing to follow house rules, and when you want a therapeutic bathing experience rather than a leisure one. It is not the first onsen to recommend to a visitor who wants a comfortable two-hour soak; it is the bath to send someone to after they have already seen Kogome no Yu and want to understand what Yugawara onsen culture looked like before day-use commercialization flattened it. Go in the morning when the water has settled, plan a short session rather than a long one, bring your own towel and ¥500 in change, and - as much as it is possible for a visitor to do this - be quiet about it.

Address: Miyakami, Yugawara, Ashigarashimo District, Kanagawa 616

Phone: 0465-62-2206

Hours: 8:00-20:00

Towels: Bring your own. Named commemorative towel sold on-site at ¥400 (vintage print that darkens after bathing - partly a souvenir). No free towels; no standard rental service.

Baths on-site: indoor bath

Source: Lot 22

Spring type: -

Source temperature: 82.8°C

pH: 8.4

Handling: source-fed hot-spring water

「時代から取り残されたような湯治場風情」

A toji-house atmosphere that time seems to have walked past.

「源泉をそのまま浴槽に投入している純粋な『源泉かけ流し』」

Pure source water piped directly into the tub - genuine flow-through.

「個人的経験では1、2を争う強さ」

In my personal experience, among the one or two strongest I've encountered.

「透き通っていて、とにかく美しい」

Crystal clear, and - simply - beautiful.

「熱すぎて、熱すぎて、身動きがとれず」

So hot, so hot, I couldn't move.

「必ず石鹸で体洗ってから湯舟に入るのが決まり」

The rule is: you wash thoroughly with soap before entering the bath.

「やけど、怪我、手術後の治療」

For burns, wounds, and post-surgical recovery.

These are points where the platforms and official pages we consulted gave us conflicting information.

• Admission pricing: Niftyonsen's structured record lists '300、100、50' - per hour. Surugabank's write-up, onsenzanmai (2023), jake.cc (2020/2023), and note.com (2024) all describe a flat ¥300 entry with no time cap mentioned. We publish ¥300 as a flat day-use fee based on the four first-person sources and treat the Niftyonsen 'per hour' field as a stale structured-data outlier. The facility has no website to cross-check against - confirm by phone (0465-62-2206) before a dated trip if the distinction matters to you.
• Bath facilities: Niftyonsen's structured profile marks open-air bath ○ for this facility. Every first-person report we consulted describes only the interior semi-basement bath and explicitly notes the absence of an outdoor element. The structured field is likely optimistic or stale; our description reflects the first-person corpus. If you arrive and find an outdoor bath, please let us know - we'll update.
• Water handling: 100% source-fed hot-spring water is claimed by the operator, confirmed by Surugabank's editorial, and in 2025 attested by Pure Onsen certification (a third-party program that verifies no water added / heated / recirculated / chlorinated). No chlorine-smell complaints surfaced in any reviewed text. The practical caveat is that source flow is limited: the bath functions as a low-turnover kakenagashi where each bather's behavior affects water quality meaningfully - which is exactly why the pre-bath washing regime is enforced.
• Tattoo policy: No published tattoo policy on any source we consulted. The operator has no website; Niftyonsen leaves the field blank; none of the first-person blog accounts mention the topic. Given the therapeutic bathing positioning, the elderly-local patron base, and the strict etiquette regime, we default to 'unknown - treat as not permitted without a direct call.' Phone 0465-62-2206 to confirm.
• Source temperature and pH: Niftyonsen lists source temperature 82.8°C and pH 8.4. Onsenzanmai reports 81.3°C, Surugabank 'approximately 80°C'; one report cites pH 8.04 as a field measurement. Variance is within normal measurement drift. We publish the Nifty structured values (82.8°C / pH 8.4) and note the directionally-consistent field measurements here.
• Parking: Onsenzanmai reports 6 free spaces; Surugabank's column mentions ¥100/hour. We cannot reconcile this without an on-site check - call ahead if parking pricing matters for your trip. Six spaces is small enough to fill on a weekend regardless.
• Day-use access: The stated operator policy is therapeutic guests only (therapeutic lodgers only); day-use is permitted in practice but not promoted, and a casual drop-in who reads as a tourist can be turned away. Approach respectfully, arrive during quiet hours (morning is best), bring exact change, follow the pre-bath washing protocol without being asked. One reviewer was admitted only after a chance street conversation with the female proprietor - treat day-use as a privilege the operator grants, not a service you purchase.

• Niftyonsen structured profile
• Suruga Bank onsen report
• KOU
• (jake.cc)
• note.com
• ohitori-onsen