As bathed in the eighteenth and nineteenth centuries and still managed to keep the decency of those times

Some clarity came only after studying the Wikipedia: Bathing machine (in Russia and Austria-Hungary was known as a bathing van) — popular in the eighteenth and nineteenth centuries, the adaptation of bathing on the seashore, allowing men and women to bathe, keeping the rules of etiquette of those times. Was a covered wagon with wooden or canvas walls. Bathing machines were a necessary part of beach etiquette, they hide the bathers from prying eyes.

The machine was lowered into the water with the horses. The popular resorts was the rails, which went down a bathing machine. In water it unfolded so that from the shore the swimmer was not visible. Then the bather went down the stairs into the water. Bathing machines were often equipped with a flag, which was raised by the bather as a signal of readiness to return to shore.

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