Wooden boardwalk crossing a green wetland in Oze, Japan

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Oze Travel Guide: Boardwalks and Wetlands in Gunma

   

Written by:

Jun

Oze is a high basin of marsh and lake in the mountains north of Tokyo, crossed by raised wooden boardwalks rather than trails. It is the largest mountain wetland in Japan, and it is a national park in its own right: Oze was separated from Nikko National Park and designated as Japan’s 29th national park on 30 August 2007, the first new designation in twenty years.

What that means for a visit is specific. There are no cars at the marsh, only at the trailheads. Access opens and closes with the snow, so the season has a start date and an end date rather than a best month. And because the ground is a floating mat of peat and moss, you walk on planks the entire way: the walking is flat, but it is long, and there is nowhere to step aside.

This guide covers the geography, the two main approaches from the Gunma side, the shuttle bus and fee situation for the 2026 season, the flower calendar, and the practical limits that decide whether Oze works as a day trip or needs a night in a hut.

Why visit

  • Oze is not a mountain to climb but a basin to cross on foot, and the boardwalk makes it accessible to people who do not hike seriously, including families with children.
  • The scale is unusual: a marsh about 6 km east to west and 2 km north to south, ringed by two distinct peaks, with the walk at roughly 1,400 m.
  • The plants are the reason most people come, in a sequence rather than all at once: skunk cabbage, then cotton grass, then day lilies, then autumn colour.
  • Access is controlled, which keeps the numbers down compared with somewhere like Kamikochi, even in the peak weeks.
  • Mountain huts inside the park let you be on the marsh at dawn, which is the hour the place is actually about.

What Oze is, geographically

The basin was formed by volcanic activity, and the marsh sits in a depression dammed by eruptive material. The two peaks that frame it are the ones you will see in every photograph: Mount Shibutsu at 2,228 m to the west, and Mount Hiuchigatake at 2,356 m to the north-east, the highest mountain north of Tohoku and a stratovolcano whose slopes hold one of Japan’s larger primeval beech forests.

Mount Shibutsu is made of serpentinite, a rock that produces poor, unusual soil and therefore a set of plants found almost nowhere else, including a species named for the place. The east trail up Shibutsu from the marsh is one-way, uphill only, for erosion reasons.

Ozenuma, the lake, is a separate body of water to the east of the marsh. It was formed when an eruption or collapse blocked the drainage, and it is smaller, quieter and reached from a different trailhead. The park also took in the Aizu-Komagatake and Taisyaku/Tadamiyama areas to the north, which are separate trips again.

  • Ozega-hara — the marsh, about 760 ha, Japan’s largest mountain wetland, between the two peaks.
  • Ozenuma — the lake east of the marsh, with its own visitor centre and its own approach.
  • Sanjo-no-taki — the waterfall where the Tadami River leaves the basin, counted among Japan’s hundred notable falls.

Top places and highlights

Wooden boardwalk crossing a green wetland in Oze, Japan
Photo: Ka23 13 · CC BY-SA 4.0 · Wikimedia Commons

The boardwalk across the marsh

The main route runs from the west edge of the marsh to the eastern huts, with junctions at Ryugu and at the Yoppi suspension bridge. Most of it is single-plank width with passing places, so the path sets the pace whether you like it or not. Signs ask you to keep to the boards, and it is not a suggestion: the peat beneath is the ecosystem, and a bootprint through it lasts for years.

Practically, the walk is flat but not short. The classic loop out to the huts and back is a full day at an unhurried pace, and the return leg feels longer than the outbound one because the views repeat.

Yamanohana and the visitor centre

Yamanohana sits at the western end of the marsh, about an hour’s walk below the Hattsutoge trailhead, and is the point where the descent from the pass levels out. The visitor centre here is staffed, carries trail and weather conditions, and runs observation sessions on some days. If you have one stop for context before walking, this is it.

Miharashi and the eastern huts

The cluster of mountain huts at the eastern end of the marsh is the overnight base for people wanting dawn on the water. It is not a village: lodgings, a small shop with limited stock, and toilets. Everything else you carry.

Ozenuma and the lake side

Ozenuma is reached from the Oze-numa trailheads on the Fukushima side or by crossing the Sanpei pass from Okushimizu on the Gunma side. The north shore has a band of small marshes and the south shore has the open water with the mountain behind it. It takes longer to reach than the marsh and is correspondingly emptier, which is the reason to choose it.

Climbing out of the basin

Both peaks are real mountains, not viewpoints. Shibutsu is a steep, exposed climb on serpentinite, with the east route from the marsh reserved for ascent. Hiuchigatake is longer and higher and, being an active-looking stratovolcano, demands a weather check rather than a plan. Neither should be attempted as an add-on to a marsh walk on the same day.

The flower calendar

Oze is usually described through three plants, and they do not overlap much.

  • Mizubasho (skunk cabbage) — late May into early June, along the marsh edges and the wet ground near Yamanohana. This is the image most people have of Oze, and it coincides with the busiest fortnight.
  • Watasuge (cotton grass) — early to mid July, when the marsh turns white in a different way: seed heads rather than flowers, moving in the wind.
  • Nikkokisuge (day lily) — July into August, in orange drifts on the drier hummocks.
  • Autumn colour — late September into October, when the grasses go gold and the birches turn, and the crowds thin out.

The dates move with the snow melt by a week or two either way. Anyone telling you a fixed week for the bloom is guessing; the park foundation publishes the season’s opening dates each spring, and those are the ones to trust.

Food and drink

There is no restaurant inside the park. The huts serve set meals to guests, and the shops at Yamanohana and Miharashi sell a limited range of drinks, snacks and sometimes simple hot food, but stock is carried in and can run out. Carry what you need for the day, plus a margin.

Water is the thing people underestimate. There are streams, but treating water in a national park is not straightforward and refill points are limited; bring more than you think, especially in July and August when the marsh is humid and shadeless for long stretches.

Before and after the walk, the onsen towns on the approach roads are where the real meals are — the Tokura area on the Gunma side has the largest cluster, and the Oze-Hinoemata side has its own soba tradition. Eating before you go up is the practical move: the trailheads have little beyond a kiosk.

Getting there and around

Oze has several entrances and they are not interchangeable. From Tokyo, the two that matter are Hattsutoge for the marsh and Okushimizu for the lake, both on the Gunma side. From Fukushima, Oike and Oze-numa trailheads serve the eastern and northern approaches.

Hattsutoge (the marsh route)

Private cars cannot reach Hattsutoge at any time of year: the Tsunagi to Hattsutoge section is closed to cars and motorcycles year-round, and no vehicle at all passes between 18:30 and 05:00. You park at Tokura, about 1,000 yen a day, and take the shared bus or shared taxi up, which costs 1,300 yen one way for adults and 650 yen for children. For 2026 the service began on 18 April. The ride is about 35 minutes; the walk from the top down to Yamanohana is roughly an hour, with stairs at the start.

Okushimizu (the lake route)

The road to Okushimizu opens in mid-April, and from 13 June to 18 October 2026 a low-emission bus ran the Okushimizu to Ichinose section, which private cars cannot use. That bus is 1,000 yen one way for adults, 500 yen for children, and parking at Okushimizu is 1,000 yen a day for 100 cars. From Ichinose it is a climb over the Sanpei pass to the lake, which is a longer and steeper day than the marsh walk.

The Fukushima side

Oike is the trailhead for Hiuchigatake and the eastern marsh, and its road opened on 24 April 2026. The Oze-numa trailhead road opened on 22 May 2026, with the electric shuttle from Oike to Oze-numa running from 23 May to 25 October 2026 at 900 yen one way for adults and 450 yen for children, a fare that rose this season. The Oze-numa rest house at the top has toilets and vending machines. This is the shortest approach to the lake, and the one to use if the lake is the point of the trip.

The cooperation fee

Gunma Prefecture ran a trial entry cooperation fee in 2026: 500 yen, voluntary, collected at Hattsutoge and Okushimizu only, staffed from 10 to 19 August and unstaffed from 11 to 20 September. It is not a legal obligation and it is not collected at Oike or Oze-numa. The money goes to boardwalk maintenance, trail repair and landscape protection, which is a fair description of what you are walking on.

Where to stay

There are three options and they suit different trips.

  • Mountain huts inside the park — at Miharashi, Yamanohana and around Ozenuma. Simple, shared, with set meals and futon. Book ahead for the bloom and autumn weeks; they are the only way to be on the marsh at sunrise.
  • Onsen towns on the approach — Tokura and Katashina on the Gunma side, Hinoemata on the Fukushima side. This is the comfortable option, and it lets you reach the first bus rather than driving in the dark.
  • Day trip from Tokyo — possible but long. The first bus up and a full marsh walk leaves little margin for a delayed train home, and the last bus down is earlier than most people expect.

A night in a hut changes the trip more than any other decision. The marsh at dawn, with mist on the water and nobody on the boards, is a different place from the same marsh at eleven in the morning.

Best time to visit

  • Late May to early June — skunk cabbage, and the busiest weekends of the year. Book transport and beds early.
  • July — cotton grass and day lilies, warmer, more stable weather, longer days.
  • Late September to mid-October — autumn colour, cooler walking, fewer people. The best balance of scenery and comfort.
  • November to April — closed. The roads shut with snow and the huts close, so there is no access regardless of fitness.

Mid-August is hot, humid and prone to afternoon storms on open ground with no shelter. If that is when you can go, start at the first bus and be off the marsh by early afternoon.

Practical tips

  • Check the season’s opening dates before booking anything. The trailhead roads open on published dates in April and May, and nothing moves before them.
  • Wear boots you can walk in for six hours, not trainers. The boards are wet in the morning and slippery in the rain.
  • Carry rain gear as a layer, not an afterthought. The basin funnels weather and there is no cover.
  • Take your rubbish out. There are no bins in the park, and the huts will not take it.
  • Use the toilets at the trailheads and the visitor centres; they are spaced further apart than people plan for.
  • Do not step off the boardwalk for a photograph. It is the one rule that matters.
  • If you are combining Oze with Nikko, note that they were one national park until 2007 and are still a long drive apart, not a single day.

Suggested itineraries

One day, marsh only

  1. Take the earliest bus from Tokura to Hattsutoge.
  2. Walk down to Yamanohana, stop at the visitor centre, and continue east along the boards.
  3. Reach the Yoppi bridge and the Miharashi junction, then turn back rather than pushing to the lake.
  4. Return up to Hattsutoge with enough margin for the last bus down.

Two days, marsh and lake

  1. Day one: in via Hattsutoge, across the marsh, overnight at Miharashi.
  2. Dawn on the marsh, then east over the pass toward Ozenuma.
  3. Day two: the lake’s north shore, down to the Oze-numa trailhead, shuttle to Oike.
  4. Bus out from Oike, or a second night on the Fukushima side.

Before you go

Bus dates, shuttle fares, hut availability and the cooperation fee all change by season, and the 2026 figures above come from the park foundation, Gunma Prefecture and the Hinoemata tourism association pages checked on 26 October 2026. Some of those services have already closed for the year; the next season’s dates are published in spring. Reconfirm the road opening date and the first bus before you commit to a date, and check trail closures after heavy rain.

Sources

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