- Oka Castle Guide: The Impregnable Hilltop Fortress That Inspired "Kojo no Tsuki"
- Discover Oka Castle in Oita, a clifftop fortress famed for inspiring "Kojo no Tsuki." Walk along unfenced stone walls with panoramic views of the Kuju Mountains.
Walking Through Oka Castle: A Clifftop Fortress Experience
Oka Castle stands 325 meters above sea level, perched atop sheer cliffs. Here, breathtaking views from unfenced stone walls await, along with the thrill of heights that makes your legs tremble.
In this article, I’ll take you through my actual walk around Oka Castle—from the parking lot to the main gate (Otemon), and all the way to the main keep (Honmaru).
For details on the history and highlights of Oka Castle, check out this article.
Read more about Oka Castle highlights
Arriving at the Free Parking Lot
The parking lot is spacious—it holds 140 regular cars and 9 buses, all free of charge.
There’s also an RV park for campers.
Purchasing Admission Tickets
Purchase your admission ticket at the ticket booth (former Soyakusho site) near the parking lot.
Admission is 300 yen for adults. Along with your ticket, you’ll receive a castle map pamphlet. You can also get your Japan Top 100 Castles stamp here.
The Path to the Main Gate
Let’s begin. It’s about 180 meters—a 2-3 minute walk—from the ticket booth to the castle entrance.
Mirror Stones (Kagami-ishi)
Along the way, you’ll notice unusually large rocks embedded in the stone walls. These are called “kagami-ishi” (mirror stones)—decorative elements that displayed the castle lord’s authority while also strengthening the wall structure.
At Oka Castle, you can find mirror stones at the main gate, the drum turret gate, and the third bailey.
Aso Welded Tuff Cliff
Oka Castle was built atop a natural rocky mountain. You can see the rock face up close.
This welded tuff was formed by pyroclastic flows from Mt. Aso’s eruptions. Over countless years, rivers carved through it, creating these sheer cliffs. You can truly feel the power of nature.
Souvenir Shop “Otemon”
Along the path to Oka Castle, you’ll find a souvenir shop called “Otemon.”
This location was once the site of the riflemen’s guardhouse.
Inside, you’ll find traditional crafts including bamboo work and woodcraft.
The sheer variety of traditional crafts is overwhelming—time flies as you find yourself wanting everything.
But first, I need to explore the castle, so I resist temptation and promise to stop by on the way back.
Heading to the Main Gate
From here, we climb the stone steps. This is the moment you feel the impregnability of this fortress with your own feet.
The steps are relatively low, so take your time and you’ll be fine.
The moss-covered stone walls evoke a sense of history. The curved stone walls are one of Oka Castle’s distinctive features.
At the switchback point of the stairs—your legs start to feel it.
There are both original stone steps and newer wooden stairs. The wooden stairs have lower steps and are easier to climb.
Looking back at the path you’ve climbed, you realize how high you’ve come.
Almost there—the main gate is just ahead.
The Main Gate and Spectacular Views Beyond
We’ve arrived at the main gate ruins. Massive stone walls greet you.
Passing through the main gate, the view suddenly opens up.
Beyond the main gate is a masugata (square enclosure). This structure prevented enemies from advancing directly—they couldn’t simply charge straight through.
Former Main Gate Ruins (Kyu-Otemon)
This is the former main gate ruins. Before the Nakagawa clan took control, this was the main entrance.
Exploring Stone Walls and Panoramic Views
From here, we explore the castle grounds. Oka Castle is extensive—expect to spend 1.5 to 2 hours if you take your time.
Nakagawa Tajimi Residence Ruins
On the way from the main gate to the main keep, you’ll find the Nakagawa Tajimi residence ruins on your left.
The scale is impressive—you can only imagine how grand the residence must have been.
The views from here are superb.
Nishinaka-shikiri Ruins (West Partition)
This is the narrowest passage in the castle—the Nishinaka-shikiri ruins.
This defensive structure forced enemies to zigzag—they couldn’t charge straight through. Walking here, you truly appreciate the ingenuity of the castle’s defenses.
Drum Turret and Bell Turret Ruins
The drum turret was the most important gate in the castle. The stone walls, built with massive stones fitted seamlessly together, symbolized the castle lord’s authority.
Third Bailey Ruins (Sannomaru)
The third bailey was where envoys from other domains and retainers met with the domain lord. Today it’s an open plaza.
Second Bailey Ruins (Ninomaru)
The second bailey has a rest area where you can take a break.
The views from the second bailey are also wonderful.
Statue of Rentaro Taki
The second bailey features a statue of Rentaro Taki. Taki spent his boyhood in Taketa and often played at Oka Castle. His famous song “Kojo no Tsuki” (The Moon Over the Ruined Castle) was inspired by this very castle.
With the Kuju Mountains behind him, he gazes into the distance—an iconic scene of Oka Castle.
Main Keep Ruins (Honmaru)
The main keep is the highest point of Oka Castle. It once housed the Honmaru Palace, the domain lord’s residence.
Here stands Okajo Tenmangu Shrine.
The views from the main keep are breathtaking.
There are no safety railings, so be careful not to get too absorbed in the views.
Shimohara Gate Ruins
The Shimohara Gate was the karamete (rear gate) of Oka Castle. Before the Nakagawa clan arrived, this was reportedly the main gate.
Seasonal Colors
Oka Castle offers beautiful seasonal vegetation. In spring, cherry blossoms—selected as one of Japan’s Top 100 Cherry Blossom Spots—are in full bloom. I visited in late March, when signs of spring were just emerging and the cherry trees were about 20% in bloom.
A Castle in the Sky Where Views, Thrills, and History Converge
Stone walls stretching across sheer cliffs, and beyond them, a sweeping panorama. Oka Castle offers an experience you can’t find anywhere else. The changing faces of seasons—cherry blossoms in spring, autumn leaves in fall—are what make you want to return again and again.
The stone steps to the main gate are a bit challenging, but the stunning views that await you are worth every step. Plan for about 1.5 to 2 hours. Be sure to wear comfortable walking shoes.