Europe's Most Jaw-Dropping Aquarium Is In A Historic WWII Flak Tower

Located in Vienna's Esterhazypark, the Haus des Meeres (House of the Seas) aquarium may appear to be an entirely modern building constructed with steel and glass. However, Nazi authorities built the structure in 1944 as a flak tower designed to protect Vienna from Allied aircraft. The 150 ft Nazi structure was one of three flak towers in Vienna and similar to fortifications built in Hamburg and Berlin. 

After the German defeat in May 1945, the L-Tower stood unoccupied until the late 1950s, when the city repurposed the relic as Haus des Meeres. Since the 1990s, Haus des Meeres has undergone numerous renovations and extensions to accommodate 600 species and 10,000 animals, including fish, reptiles, amphibians, birds, and mammals. Awarded the Vienna Tourism Prize in 2017, the Haus des Meeres continues to go from strength to strength and recorded an all-time high of 930,000 visitors in 2023. Before driving three hours to the majestic Grüner See in the Austrian Alps or cruising down the Danube, allow this unique 11-floor aquarium to bring nature to you. 

Haus des Meeres is first and foremost an aquarium but the 53,819-square-foot building is also home to various land creatures. The tropical, jungle, and reptile areas house everything from marmosets and red-eyed tree frogs to water monitors and chameleons. Endearing and curious though these animals may be, the aquarium's marine life remains the leading attraction for most visitors. 

Almost all of the Haus des Meeres' 11 floors host sea creatures of some kind, including clownfish, Japanese spider crabs, turtles, Lionfish, guitarfish, and many others. For some, the aquarium's main event is the 360° shark tank on the seventh floor, which replicates an Indo-Pacific coral reef and hosts blacktip reef sharks, zebra sharks, blue-spotted masked rays, and four different species of surgeonfish. Haus des Meere might not have the sheer size of some of the world's largest aquariums, such as L'Oceanogràfic in Spain, but it is a fascinating site, worthy of anyone's Vienna itinerary. 

The repurposed flak tower gives a zoological experience like no other, for it doubles as both an animal enclosure and an observatory with 360-degree views of Vienna's domes, churches, and perhaps even Vienna's excellent wine gardens. Where else can one befriend rosella parrots and white-faced sakis while looking over the historical buildings of a European capital? This is something even America's best aquariums can't offer. 

These views are even better on the top floor, where you'll find the 360°Ocean Sky restaurant and bar with a panoramic terrace and a kitchen serving regional dishes including spaetzle, Viennese soup, and apple strudel. For another perspective of this unusual building, try climbing its south wall. The Austrian Alpine Club installed a climbing wall here in 1998, covering its 7,534-square-foot surface with over 4,000 holds that offer 20 routes with difficulty levels ranging from four to eight.

And if you're less of a thrill seeker and more of a history buff, Haus des Meeres does not attempt to hide the location's dark past. A history exhibition occupies part of the 10th floor explaining the tower's original military purpose, displaying numerous artifacts including an all-wave receiver, an air raid siren, and a collection of clothing and documentation.