Although the other side of Gellért Hill attracts more visitors the northern slope also offer various sights worth visiting. One of them is Gruber József Cistern, the largest cistern of Budapest.

Gruber József Cistern was named after the notable mechanical engineer and university professor József Gruber. As an outstanding character of engineering he held several titles such as the Adjunct Professor of the Institute of Aerodynamics, Head of Dept. of Fluid Mechanics, Dean of Mechanical Engineering Faculty and also the Rector of Budapesti University of Technology and Economics.

Apart from a pipe system built during the reign of King Matthew in the 15th century the first water supply network was established in the 19th century. Central water supply started only in 1868 in Budapest replacing water carriers. Continuous shortage of water required a central cistern of a large capacity. The uninhabited eastern slope of Gellért Hill was an ideal spot being centrally located and high enough to use gravity in water distribution.

The cistern went into service in 1903. Water shortage still being an issue a much larger cistern was built between 1972 and 1980. The two cisterns are connected with a one-kilometer-long tunnel.

The cistern plays a key role in the water supply of Budapest as daytime water need is satisfied from the cistern filled up by night. It also contributes to water pressure control and serves as an emergency storage facility also.

The new cistern was a masterpiece of engineering at the time. The piano-shaped design of the two chambers assures continuous and consistent water flow preserving water quality. Water first arrives to the pumps station in Békásmegyer (North Buda, District 3) from wells of Szentendrei Island and Csepel Island and then it is pumped to the cistern inside Gellért Hill. The two chambers have a capacity of 40.000 m3. The ceiling is held by 106 columns with conic ends. The cisterns cover an area of 5000 sqm. The cistern welcomes visitors on open days when water is drained.

Visit the Garden of Philosophy and the Sculptures of Kilátókő atop the cistern that offer a scenic view over the city.