From Stamps of the World
Heenvliet is a town in the Dutch province of South Holland. It is a part of the municipality of Nissewaard, and lies about 7 km south of Maassluis, on the Brielse Maas. Heenvliet was a separate municipality until 1980, when it became part of Bernisse.
Read more @ https://en.wikipedia.org/wiki/Heenvliet