Gruba Kaśka

The model of Gruba Kaśka represents a structure standing in the Vistula. Its real counterpart is an infiltration well, not an observation tower or a storehouse: it collects water that seeps through natural layers of sand and gravel beneath the riverbed.

Construction began in 1953, and the first water reached Warsaw's taps in September 1964. The system uses riverbed infiltration, which provides initial filtration as water passes through the sediments.

Fifteen drains, or perforated pipes, radiate out around the well. They draw water from about seven metres below the bed of the Vistula, so much of the system lies out of sight rather than above the river's surface.

The collected water enters the well, where pumps send it onward for further treatment. The visible structure is part of an installation connected to the right bank by a tunnel, construction of which began in 1960.