Kalkar is a town in Aedirn that first appears on a map of the Pontar Valley in The Witcher 2: Assassins of Kings. Its located near the Pontar River.
Geralt decisions will have an influence over the question whether the city becomes part of Saskia's Free Pontar. Otherwise Kaedwen will annex it together with the rest of the valley.
Kalkar is the name of a German town not far away from the Dutch border.