Zámecký pramen, Mineral spring at Tržní kolonáda, Karlovy Vary, Czech Republic.

Zámecký pramen is a single mineral spring in Karlovy Vary, diverted into two outlets: Zámecký dolní (spring no. 3) on the Tržní kolonáda and Zámecký horní (spring no. 4) on the elevated Zámecká kolonáda. Both outlets are freely accessible and flow at 43 °C, with yields of 0.9 l/min and 0.6 l/min respectively, each containing 600 mg/l of CO2.

Discovered in 1769 beneath the Castle Tower on Tržiště, the spring was first captured in 1797, when it flowed 14 metres above Vřídlo. Its outlet vanished after the Vřídlo explosion of 2 September 1809 and returned on 15 October 1823. A first colonnade was built over it in 1830, replaced in 1910–1912 by Friedrich Ohmann's Art Nouveau Castle Colonnade.

This spring is part of the spa town's daily ritual where visitors taste the warm mineral water from traditional porcelain cups while strolling through the colonnade area. The drinking of water directly from the source remains a central part of how people experience the town's wellness culture.

The spring is accessible on foot from the town center but is situated in an area with sloped pathways and uneven ground. Comfortable walking shoes are advisable since reaching the spring and exploring the surrounding colonnades requires some elevation changes.

In the freezing winter of 1784, when all the town's wells froze, this warm spring was piped into the public fountains. Its deposits later led physician Dr. David Becher to analyse the water and find it had the same composition as Vřídlo.