Katwijk is a coastal municipality and town in the province of South Holland in the western Netherlands. Katwijk is located on the North Sea, northwest of Leiden and 16 km north of The Hague. The municipality is essentially the area between Leiden and the North Sea. Katwijk lies along the Oude Rijn, which ends at the North Sea in Katwijk aan Zee. It shares its borders with the municipalities of Noordwijk, Teylingen, Oegstgeest, Leiden, and Wassenaar. Katwijk is by far the largest town in the Duin- en Bollenstreek ("Dune and Bulb Region"). The municipality covers an area of 31.06 square kilometers (11.99 mile²), of which 6.41 square kilometers (2.47 mile²) is water.