With a splendid underground cathedral-like structure, colourful mosaic-style tiles and a spiral staircase, the Kőbánya Water Reserve is a sight in its own right. Because of its function, supplying Budapest with drinking water, it is always off-limits to the public, except for one day a year: European Heritage Day this Saturday.

The Kőbánya Water Reserve has been supplying Budapest with drinking water for nearly 150 years now. Its building – a genius work of engineering, designed by Italian experts – is stunning. It looks for all the world like an underground cathedral with arches, tall columns and many-hued mosaic-like bricks on the walls that are further colourised by the water.

Visiting the water reserve is a special experience, and since it is only drained and opened to the public once a year, something that is totally unmissable. Admission on Saturday is free and there's no need to register – only smaller groups will be allowed inside at any one time, so you may have to queue for a little bit.

Kőbánya Water Reserve (Kőbányai víztározó)

District X. Ihász utca 29

Saturday, 21 September 9am-4pm

Admission: free

How to get there: From Örs Vezér tere or Kőbánya-Kispest, take bus 85 to Ihász utca, or bus 95 from the Puskás Ferenc Stadion to Kápolna tér.