The unkai phenomenon is caused by a significant temperature difference between the valley and the mountaintop.
Takeda Castle is often referred to as the 'Machu Picchu of Japan' due to its placement on a mountain ridge.
The observation deck overlooks the Maruyama River valley, which traps humidity to form the fog layer.
Ritsuunkyo features three distinct observation decks, with No.1 being the lowest and most frequently visited.
The No.1 Observation Deck, located within the Ritsuunkyo mountain park, provides the primary vantage point for viewing the 'Castle in the Sky' effect of Takeda Castle. It is positioned on the mountainside directly opposite the ruins, allowing observers to see the castle floating above a dense sea of clouds known as unkai. The deck is reached via a series of stone steps and trails from the Ritsuunkyo parking area. During optimal weather conditions, the site offers a panoramic view of the 15th-century castle ruins encapsulated by morning mist. This specific observation point is the most accessible of several viewpoints along the mountain slope.
The very center of the No.1 Observation Deck platform provides the most direct line of sight to the castle ruins.
Bring a high-quality tripod, as the low light during early morning hours requires long exposure times.
Wear sturdy hiking footwear, as the path from the parking area to the deck is unpaved and can be muddy.
Check local weather forecasts for high humidity and low wind speeds, which are prerequisites for the cloud sea.
Do not attempt to walk to the deck in sandals or formal footwear; avoid visiting on windy or dry days when the cloud sea is unlikely to form.
The area is open year-round, though access may be restricted during severe weather or heavy snow events.
Maintain silence to respect other photographers and nature; pack out all trash.
