Forest in the Water Aquarium (Fuji Yusui-no-Sato)

Set in the village of Oshino between Lake Kawaguchi and Lake Yamanaka, the Forest in the Water Aquarium — officially the Yamanashi Prefectural Fuji Yusui-no-Sato Aquarium — is a small but genuinely charming attraction that showcases the freshwater fish of Japan's rivers and lakes, all sustained by the pure spring water that filters down from Mt. Fuji. It is Japan's largest aquarium dedicated to freshwater species, and its setting amid a landscaped water park makes it feel more like a woodland pavilion than a conventional aquarium.

The building's signature feature is its clever 'double tank' architecture. The main tank is nested inside a larger outer tank, so that when you look through the fish you also see fish swimming in the water beyond — creating an unusual layered, three-dimensional view that gives the impression of peering into a living river rather than a glass box. It is a simple idea, beautifully executed, and it makes even familiar species look striking.

The collection focuses on the fish of Fuji's watershed and Japan's freshwater habitats: trout, char, salmon, koi, sturgeon, catfish and a variety of native river species, along with some rare and endangered types the prefecture works to protect. Because the aquarium draws on Mt. Fuji's famously clean, cold spring water, the tanks have a clarity that is striking in itself, and interpretive panels explain the local aquatic ecology and conservation efforts. It is compact enough to see thoroughly in about 45 minutes, which makes it ideal for families with young children or as a relaxed indoor break.

What elevates the visit is its immediate surroundings. The aquarium stands within the Sakasa-gawa Freshwater Park, a pretty green space threaded with clear streams, and just a short stroll away lies Oshino Hakkai, the celebrated cluster of eight spring-fed ponds where snowmelt from Fuji rises in pools so transparent they look almost invisible. Together they make a lovely half-day of water, greenery and — on clear days — Mt. Fuji rising behind the village.

Historically and environmentally, the aquarium reflects Yamanashi's pride in its Fuji-fed water, which is bottled commercially and revered locally for its purity; the facility doubles as an education centre about protecting those aquatic resources.

The visiting experience is easy and unhurried: the building is single-level, step-free and quiet compared with the big lakeside sights, with restrooms, a small gift shop and free parking on site. It works in any weather and is an especially good option on rainy or very hot days. To reach it, take a bus or taxi from Fujisan Station toward Oshino Hakkai and get off nearby, or drive — the free parking at the freshwater park makes it simple. Combine it with an Oshino Hakkai walk for one of the most relaxed and photogenic outings in the Fuji Five Lakes.