Aquarium

Aquarium of the Antwerp Zoo, Belgium.
It's build from 1905 until 1910 (first use in january 1911). Above the aquarium building you have the reptile building of the zoo.

Is that one large tank behind those panes..?

@ NZ Jeremy: the aquarium building was renovated in 2007 and 2008. The tanks are now at some places twice as deep and much larger. Largest tank is 3 or 4 panes long. The zookeepers now can walk on a special construction above the tanks. It's an old building so they fixed it very well!