Fat Kaśka

'Fat Cathy') is the popular name for an 18th-century neoclassical water well in central Warsaw, Poland.

It is situated at Solidarity Avenue (Aleja Solidarności), close to the intersection with Andersa Street.

It is decorated with rusticated panels and has a stepped roof crowned with a gilded ball.

Immediately after the war, from 1947 to 1949, the road around it (then Leszno Street) was widened for the construction of the Warsaw W-Z Route.

A renovation in 2004 restored its original appearance, including exposing formerly bricked up windows and strengthening its foundations.