Hungerbrunnen, Natural monument spring in Gerstetten, Germany

Hungerbrunnen is a periodic karst spring on the flat floor of a dry valley on the Schwäbische Ostalb, at about 523 m above sea level, 400 m northwest of where the Altheim–Heuchlingen road crosses the valley. Its water runs only about 70 m into the usually dry trench also called Hungerbrunnen, which continues southeast through the 8.5 km long, 50–90 m wide Hungerbrunnental toward the Lone. When dry, it is easily missed: look for the roughly 5 m long gravel bed and the outflow channel cut across the meadow.

At the spring, the territories of Altheim (Imperial City of Ulm) and Heldenfingen and Heuchlingen (Duchy of Württemberg) met; a small neutral square there served as a place of refuge. Ulm council documents from 1533 record that the communities alternately held a festive day with a small market and dances on Easter Monday and the first two Sundays after Easter. Around 1730 Württemberg and Ulm jointly abolished the festival, but young people still gathered there on Palm Sunday.

The name comes from the irregular flow: people once read the spring as a menetekel warning of poor harvests, famine, inflation or war. From 1533, Ulm records show Altheim, Heldenfingen and Heuchlingen held a market and dance day there alternately on Easter Monday and the two following Sundays, until Württemberg and Ulm abolished the festival around 1730; young people still come on Palm Sunday.

The spring usually runs dry; when it flows, the water often sinks back into the ground within two kilometres. The roughly 5-metre gravel bed and the runoff channel crossing the meadow are easy to miss from the road, so approach on foot. The source lies 400 metres north-west of the Altheim–Heuchlingen road crossing.

The spring's irregular flow was once read as a menetekel, a warning of crop failures, famine, rising prices or war. The 1844 Oberamt Heidenheim description records that flow usually followed a very wet summer and autumn and lasted one to two years, and that in the previous century it was said to have flowed for seven years in a row.