Mt. Bounoore (969m) Hiking Guide — Gorge Scrambling Along the Shiraya-sawa Stream

Trail Overview

Mt. Bounoore (棒ノ折山, Bō-no-ore-yama), also known as Bō-no-mine, stands at 969m on the border of Hanno City (Saitama) and Okutama Town (Tokyo). It has earned a devoted following among Tokyo hikers for its spectacular stream-side trail through the Shiraya-sawa gorge — one of the most adventurous day-hike experiences within easy reach of the capital.

The gorge section (gorju) is the main attraction: a narrow ravine where rock walls rise on both sides of the stream, and you advance using chains, ladders, and stepping stones across the rushing water. Once past the gorge, the trail mellows into a pleasant ridge walk leading to a grassy summit with views over Lake Naguri (Arime Dam).

From Ikebukuro, take the Seibu Ikebukuro Line to Hanno Station (about 50 minutes), then a bus to Sawarabi-no-Yu (about 40 minutes). The popular loop route ascends via Shiraya-sawa and descends along the Taki-no-taira ridge. Waiting at the finish is Sawarabi-no-Yu hot spring, right at the bus stop.

Recommended Route

The most popular loop starts at Sawarabi-no-Yu, ascends via Lake Naguri and the Shiraya-sawa gorge, then descends the Taki-no-taira ridge back to the start.

Course Time

Section	Duration
Sawarabi-no-Yu bus stop → Lake Naguri (Arime Dam)	15 min
Lake Naguri → Shiraya-sawa trailhead	10 min
Trailhead → Gorge section	30 min
Gorge section → Iwatake-ishi boulder	40 min
Iwatake-ishi → Mt. Bounoore summit	30 min
Summit → Iwatake-ishi (descent)	20 min
Iwatake-ishi → Taki-no-taira ridge → Sawarabi-no-Yu	70 min
Total (loop)	About 3 hr 35 min (excluding breaks; allow ~4.5 hours total)

Tip: Always take the Shiraya-sawa route going UP. Descending through the wet gorge dramatically increases the risk of slipping. Use the dry Taki-no-taira ridge trail for the descent.

Trailhead Facilities

Convenience Stores & Shops

• Seven-Eleven near Hanno Station: About 1 minute from the north exit. Stock up here — there are no shops at the trailhead
• Sawarabi-no-Yu: Light snacks and vending machines available at the hot spring facility
• Lake Naguri (Arime Dam) area: No shops or vending machines. Prepare everything at Hanno Station

Restrooms

• 🚻 Hanno Station: Inside the station building
• 🚻 Sawarabi-no-Yu: Restrooms inside the facility (during opening hours)
• 🚻 Lake Naguri (Arime Dam): Public restroom at the dam site
• 🚻 Mt. Bounoore summit: No restroom at the summit

Important: There are no restrooms between the dam and the summit. Use the facilities at the dam before starting your climb.

Highlights

Shiraya-sawa Gorge

The star attraction of Mt. Bounoore. Towering rock walls close in overhead as you scramble upstream using chains and iron ladders, crossing the stream on stepping stones. The combination of rushing water, overhanging cliffs, and dappled sunlight creates a dramatic, almost other-worldly atmosphere. It feels like a taste of real canyoneering on a marked hiking trail.

Lake Naguri (Arime Dam)

You’ll pass this reservoir on your way to the trailhead. The cobalt-blue water framed by surrounding mountains makes a beautiful scene. From the summit, you can look down at the lake nestled in its valley — one of the most rewarding views on this hike.

Grassy Summit Meadow

The summit is an open, grassy clearing with benches — perfect for spreading out a picnic. The views stretch across the Oku-Musashi and Okutama mountain ranges, offering a satisfying sense of space and accomplishment.

Iwatake-ishi Boulder

A massive rock about 5 meters tall marking the junction of the Shiraya-sawa and Taki-no-taira ridge routes. It serves as the landmark for the loop route’s turning point.

Tips & Safety

• ⚠️ Never enter Shiraya-sawa during or after heavy rain: The stream can flood rapidly, making crossings extremely dangerous. Check the weather forecast carefully and choose another route if conditions are poor
• ⚠️ Slippery wet rocks: The gorge rocks are perpetually wet and mossy. Waterproof hiking boots with aggressive tread are essential — sneakers are not safe here
• ⚠️ Chains and ladders: The gorge section has fixed chains and iron ladders. Use the three-point-contact technique and take your time
• ⚠️ Go up the gorge, not down: The Shiraya-sawa route should only be used for ascending. Descend via the Taki-no-taira ridge to avoid dangerous downclimbing on wet rock
• ⚠️ Limited bus service: Buses to Sawarabi-no-Yu run only 1-2 times per hour. Check the return schedule before you start hiking
• 🐻 Bear country: The Oku-Musashi area is home to Asian black bears. Carry a bear bell