Panoramic view of a 19th century Belgian reservoir

This is an eerie and cool panorama of a 19th century Belgian reservoir, temporarily drained for maintenance: "The tank is normally filled with water and therefore inaccessible.
Built in 1877, it collects the water collected by galleries "draining" of the Bois de la Cambre and the Foret de Soignes.
Its storage capacity reached 18,000 m³."

The water tank of Etterbeek / Le Reservoire d'eau d'Etterbeek

(Thanks, Jeffrey!)