The "St. Martin's Spring", the correct name of the ferruginous acidulous well on the Altengärtenweg, was first tapped in 1742 and has been available to the population as valuable drinking water free of charge ever since. Many hikers and cyclists take the opportunity to fill up their bottles here.

Today's graceful fountain pavilion with its cast-iron columns was erected in 1890 by Baron Heinrich von Kusserow, who had married an adopted daughter of the Abraham von Oppenheim couple. When the corrugated iron of the octagonal well tube began to rot near the ground, the structure received a 35cm thick and 75cm high plinth masonry in 1952.

In 1985, the municipality bought the entire castle grounds from the Waldthausen administration. During the 1986 renovation, the plinth wall was removed and the original condition was restored with new corrugated sheet metal, which had to be worked out by hand. Thus the fountain pavilion has been restored to its former beauty. The acid well is regularly analysed and tested for pollutants. According to experts, the water is healthy and of excellent quality.