Katsuura Undersea Park is a marine park located in Katsuura City, Chiba Prefecture, where visitors can experience the rich natural environment of the Pacific Ocean. The park was designated as Japan’s 40th marine park in June 1974.
The surrounding coastline forms part of the Minami-Boso Quasi-National Park and is characterized by a ria coast, with rugged rocky shores, steep wave-cut cliffs, and numerous small inlets. The waters are home to a wide variety of marine life, including sea urchins and abalone.
The protected marine area covers approximately 14.5 hectares, encompassing both the coastal landscape and underwater ecosystem.
The designation as a marine park helps protect marine resources and the natural coastal landscape while providing opportunities for visitors to experience and learn about the ocean environment.
One of the park’s major attractions is the opportunity to observe not only marine creatures but also the diverse underwater landscape, including rocky formations, wave-eroded cliffs, and sandy areas.
The Underwater Observation Tower stands approximately 60 meters offshore. The tower is 24.4 meters high, and visitors descend a spiral staircase from sea level to an underwater observation room located approximately 8 meters below the surface.
The tower is connected to the shore by a pier. During clear weather, the walk toward the tower provides expansive views across the Pacific Ocean and toward the distant horizon.
The underwater observation room has 24 windows positioned to allow visitors to look into the surrounding sea. Approximately 90 species of marine life may be observed throughout the year, although the species and visibility naturally vary with conditions.
Colorful fish such as Moorish idols and cowfish can sometimes be seen alongside species familiar as food fish in Japan, including striped beakfish and rockfish.
Visitors may also be fortunate enough to encounter a banded houndshark measuring around 1.5 meters in length. The meeting point of warm and cold ocean currents contributes to the area’s diverse marine ecosystem.
At the top of the tower, an outdoor observation area provides a 360-degree panoramic view of the Pacific Ocean.
On exceptionally clear days, the horizon can appear to curve gently across the vast expanse of ocean. Finless porpoises, a small species of toothed whale, have also occasionally been spotted in the surrounding waters in recent years.
The Museum of the Sea, a branch of the Chiba Prefectural Central Museum, opened in March 1999. The museum introduces the marine environment and geological features surrounding the Boso Peninsula.
Its exhibitions are organized into four main sections: “The Seas of Boso,” “The Many Faces of the Sea,” “Nature Surrounding the Museum,” and “Playing with the Sea.”
Visitors can learn about the region through geological models, video presentations, specimens, and aquarium displays.
In addition to exhibitions, the museum conducts surveys and research into marine organisms and environmental conditions in the surrounding waters. The results are presented through panels, videos, and other educational materials.
The museum has a relatively specialized focus, so its number of exhibits is limited, but the detailed explanations make it particularly interesting for visitors who want to learn more about the natural science of the Boso coast.
Several special exhibitions are held each year, providing opportunities to discover the latest findings from research in the surrounding marine environment.
Fujiya opened on the second floor in front of the Underwater Observation Tower ticket counter in July 2022. The shop serves Okinawan-style red-bean desserts, shaved ice, and light meals.
It is a convenient place to take a break after exploring the park, especially on warm days when a cold dessert can be particularly refreshing.
Also opened in July 2022, edén is a resort-style facility designed to combine dining and relaxation.
The first floor features a Mediterranean restaurant where visitors can enjoy creative dishes made with local ingredients. The second floor features a natural hot-spring spa using water brought from Kominezu Hot Spring.
The spa also includes a pool and sauna, providing a place to relax while enjoying views of the ocean. With its architecture and setting blending into the surrounding inlet, the facility creates a peaceful atmosphere reminiscent of a seaside paradise.
The waters off the Ubara area of Katsuura are surrounded by the rugged landscape of a ria coast. Steep rocky formations, headlands, and small inlets create a dramatic coastal landscape.
Various coastal plants grow around the cliffs and inlets, adding seasonal color to the scenery. The wave-cut cliffs and rock formations can also be viewed from sightseeing boats and kayaks, providing a different perspective on the coastline.
The rocky shorelines around the area are popular places for tide-pool exploration. At low tide, visitors can carefully explore shallow pools and observe small creatures such as crabs, hermit crabs, and sea slugs.
Watching the changes brought by the rising and falling tide offers an enjoyable introduction to the way coastal ecosystems function.
The nearest major expressway interchange is the Ichihara-Tsurumai Interchange on the Ken-O Expressway. From the interchange, the journey takes approximately 90 minutes via National Routes 297 and 128.
The parking area in front of the Museum of the Sea can accommodate approximately 170 regular vehicles and 7 large vehicles. Parking is free.
From Katsuura Station on the JR Sotobo Line, the park can be reached in approximately 7 minutes by taxi.
Visitors can also take a Kominato Bus bound for Undersea Park Center and get off at the final stop. Bus services are relatively limited on weekdays but are increased on weekends and public holidays.
Another convenient option is Ubara Station on the JR Sotobo Line, which is approximately a 10-minute walk from the park.
In spring, azaleas, rhododendrons, and other flowers bloom around the inlets and walking paths. The air is often clear, making it an attractive season for enjoying the views from the observation tower.
Summer is an excellent time to explore the underwater observation tower and rocky shoreline. The marine environment provides a refreshing alternative to simply spending time on a conventional beach.
Visitors exploring the coast should take care to stay hydrated and pay close attention to changing sea and weather conditions.
In autumn, the setting sun can illuminate the surface of the Pacific with warm golden light. From the observation tower, the broad horizon creates an especially atmospheric view.
Changes in water temperature can also affect where different fish gather, making underwater observation an ever-changing experience.
Winter tends to be a quieter season, and visitors may sometimes have the observation tower almost to themselves. Although the coastal wind can be cold, clear winter conditions can provide excellent underwater visibility.
Katsuura Undersea Park offers a unique combination of marine observation, natural scenery, education, dining, and relaxation.
The Underwater Observation Tower allows visitors to look directly into the sea without having to dive, while the Museum of the Sea provides a deeper understanding of the marine environment and geology of the Boso Peninsula.
Outside the facilities, the rugged ria coastline, rocky shores, tide pools, and seasonal scenery provide additional opportunities to experience nature.
For travelers interested in marine life, coastal landscapes, nature, and unique sightseeing experiences, Katsuura Undersea Park is an excellent place to discover both the world above the Pacific and the fascinating ecosystem hidden beneath its surface.