Nerija Fort: from guns to fish tanks

Nerija Fort also known as the Kopgalis Fortress is a 19th-century Prussian coastal fortification located on the Curonian Spit in Klaipeda, Lithuania, which was masterfully transformed into the Lithuanian Sea Museum. Opened in 1979 after several years of reconstruction, the project was famously developed "illegally" by local architects and historians who bypassed rigid Soviet bureaucratic prohibitions on building new entertainment venues by disguising the world-class aquarium as a heritage fortress restoration.

Today old bastions house a world-class aquarium and dolphinarium that perfectly blend military heritage with marine science. The Nerija Fort transformation is a great example of how a place of war can become a place of peace thanks to the extraordinary enthusiasm, persistence, and ingenuity of a team of enthusiasts.

In 1865, the Kingdom of Prussia began building a coastal fort on the northern tip of the Curonian Spit, directly across a strait from Klaipeda, then known by its German name, Memel. Its purpose was to defend the entrance to the city’s port and its outer roadstead against attack from the sea.

Known as the Kopgalis Fortress or Nerija Fort, the complex was completed in 1871. It consisted of a six-sided defensive rampart, underground casemates and powder magazines, a moat, and a two-storey circular redoubt at its centre.

Yet the fort's cannons never fired a shell. Even as its defences were being improved, advances in naval artillery were making traditional coastal fortifications increasingly obsolete. In 1897, the fort’s guns were dismantled.

This was the first transformation of the site from a place of war to a place of peace—and it would not be the last.

The transition began before the fort was fully disarmed. A village school operated in one of its casemates from 1879 to 1900. Other rooms became storage spaces, and port workers and their families lived in the complex. In 1902, a maritime semaphore and signal station was installed on the northern rampart to communicate weather and sea conditions to vessels approaching the port.

The fort continued to change hands as the political map of the region shifted. Klaipeda became part of Lithuania in 1923, was annexed by Nazi Germany in 1939, and put into Soviet control in 1945.

During the Second World War, the Nazi German Navy used the fort as an ammunition and ordnance store. As Soviet forces advanced on Klaipeda, retreating German troops destroyed the central redoubt and the bridge over the moat in January 1945, leaving the site badly damaged.

The Soviet border guards subsequently took over the fort or what's left of it. Situated in a restricted border zone, it remained closed to the public until 1975. Its surviving walls, tunnels and casemates were left to the elements, while the ruined centre became an unlikely candidate for a very different future.

The idea of turning the abandoned fort into a sea museum took shape in 1969. The leading figures were Alfonsas Žalys, chairman of Klaipeda’s Executive Committee, and Petras Lape, an architect working in the city’s urban construction design system. The reconstruction team also included architects Laima Šliogerienė and Vytautas Šliogeris, with Tautvydas Tubis as technical designer. The project brought together people with very different skills: architects, engineers, historians, biologists, sailors, industrial workers and city officials.

The obstacles were not just architectural. Under Soviet central planning, building a new public attraction of this kind was formally prohibited. Historian Eglė Rindzevičiūtė’s research describes the project as formally illegal under an all-Union restriction on what were called “spectator venues”.

Rather than immediately creating a new, independent institution, the project was smartly developed through the existing Klaipeda Local History Museum. The work at Kopgalis was presented as the restoration of a partly destroyed historic fortress rather than the construction of a major new public attraction.

The site’s location in a guarded border zone, separated from the city by the busy port, also made the physical work less visible. Žalys’s position gave the project crucial local backing and access to influential decision-makers in Soviet Lithuania but the project's masterminds still had to be discreet about what they were doing.

The resulting museum was neither wholly a product of the Soviet system nor simply an act of resistance to it. It emerged from the uneasy combination of both.

Restoration work began in 1974 and continued for several years.

Designing an aquarium inside a historic fort was one thing. Making it work was another. There was little readily available information in Soviet Lithuania about constructing a modern marine aquarium. Foreign expertise was difficult to access, and the project could not simply copy an existing Soviet model.

Architect Petras Lape therefore turned to a personal contact: his brother, who lived in the United States. He asked him to find literature about American marine aquariums. The brother eventually sent a small booklet about the New England Aquarium in Boston, which had opened in 1969. It was not a set of construction drawings, but it offered an insight into how such a facility had been arranged.

One detail immediately concerned Lape. The water-filtration plant depicted in the booklet appeared to be several times larger than the aquarium itself. Building a comparable industrial structure beside the historic fort would have overwhelmed the fragile landscape of the Curonian Spit.

Lape and Tubis consequently had to develop a more discreet solution. Rather than relying on a conspicuous filtration building, the system would draw water directly from the Baltic Sea and pass it through natural sand filters before sending it to a reservoir. The water could then be treated and its salinity adjusted for the needs of different aquarium inhabitants.

The engineering challenges did not end there. Seawater is corrosive, and conventional galvanised metal pipes were unsuitable for a system expected to operate for years. Plastic pipes, joints and valves were difficult to obtain at the time. The team also had to work out how to make reinforced-concrete structures that could withstand prolonged exposure to seawater.

The aquarium was therefore not simply a restored historical building with fish tanks installed inside. It was a custom-engineered facility whose materials and systems had to be adapted to circumstances in which even commonplace construction supplies could become obstacles.

One particularly revealing episode involved the roof over the aquarium courtyard.

The construction team initially expected to leave the courtyard uncovered. But the decision was eventually made to roof the area above the pool, creating another challenge: where could they obtain the steel roof trusses?

Four factories in Klaipeda agreed to manufacture them. Because this was not part of their normal production plans, the factories drew steel from their own reserve stocks. The arrangement depended heavily on the willingness of local managers and workers to cooperate with the project.

There was, however, a catch. Each factory produced trusses with a different structural profile. When the pieces arrived at Kopgalis, they did not form a uniform set that could simply be assembled according to one standard design.

Petras Lape once again had to come up with a solution. He designed an aluminium roof structure, which required the team to secure a separate allocation of aluminium from a factory in Voronezh in central Russia.

The episode captures the character of the entire undertaking. The problem was solved through improvisation, personal coordination and the ability to redesign around whatever materials could actually be obtained.

Once the building began to take shape, the museum faced another question: what would it display?

The collection had started years earlier, when Klaipeda’s Local History Museum established a maritime section in 1967. The early displays included objects connected with shipping and fishing, navigation instruments, ship models, and a borrowed collection of seashells belonging to Feliks Rimkevičius, a pilot working at Klaipeda port. As the project developed, the museum began acquiring preserved marine specimens as well as historical objects.

Aloyzas Každailis, a historian and a man of many talents who was on the project team, together with his colleagues soon realised that ordinary museum acquisitions would not be enough. To build a substantial collection of marine fauna, they would have to travel with the fishing fleet.

The first major expedition took place in April–June 1975, when Každailis and museum biologists joined Lithuanian fishing vessels on a voyage to the central North Atlantic. The researchers were formally attached to the ship’s crew and worked with the fishermen to collect marine specimens from their nets. For the crew, many of these creatures were unwanted bycatch; for the museum, they were valuable exhibits. The researchers selected crustaceans, echinoderms, molluscs, fish and other marine organisms, which were frozen for the journey back to Klaipeda and subsequently prepared for display.

There would be further voyages and contributions from the industrial fishing fleet. The museum’s collection grew through a combination of fieldwork, donations, salvaged maritime equipment and the work of biologists and preparators. The aquarium was designed to accommodate freshwater fish, Baltic species and fish from tropical seas. Over time, the museum’s animal displays expanded to include penguins, seals and sea lions, alongside the fish and other organisms in its aquariums.

The museum opening eventually took place on 28 July 1979. Aloyzas Každailis, who had been developing the city’s sea museum collection since the early 1970s, became its founding director and one of its driving forces.

The surviving fortifications had been restored and adapted for public use, while a new circular aquarium building occupied the site of the redoubt destroyed in 1945. Visitors could explore the former casemates and underground passages, now used for exhibitions on Lithuanian seafaring and marine life.

The museum’s transformation was not yet complete. The next stage would bring live dolphins to Kopgalis—but it would take another 15 years before the dolphinarium officially opened...

The Sea Museum continued to grow. Its historic casemates tell stories of Lithuanian shipping, while the aquarium introduces visitors to marine life from the Baltic and beyond. The dolphinarium added a new attraction, and later developments expanded the museum’s educational and research activities.

At the museum’s 40th-anniversary celebrations in July 2019, director Olga Žalienė reflected on the people and place that made the project possible:

“Here, at the tip of the Curonian Spit, land, sea, the lagoon and people meet. I very much doubt that the Lithuanian Sea Museum would have come into being and grown without Alfonsas Žalys, the Klaipeda city leader of the time, and Aloyzas Každailis, the historian who founded the museum and served as its director for many years. The ruins of an old Prussian fort have become a Lithuanian jewel, where aquatic life flourishes and stories are told about how people live by the sea and in it.”

By that anniversary, approximately 24 million visits had been recorded—a remarkable achievement for an institution that began as an ambitious idea for a remote, ruined military site.

The story of Kopgalis is not simply one of restoring an old fortress. It is a story of turning a place associated with military power into a public institution devoted to maritime history, science and education.

The transformation required political persistence, engineering ingenuity, help from fishermen and factory workers, and the determination of people who refused to let a difficult idea remain only an idea.

In that sense, the old fort’s journey from guns to fish tanks is a particularly vivid example of swords being beaten into ploughshares.

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