Pertisau is a small village on the Achensee Lake in the Tyrol region of Austria. Pertisau is in the Schwaz. It is located in the Karwendel Alpine Park, one of the oldest, cross-border, protected areas of the Eastern Alps. The town was used by English school story writer Elinor M. Brent-Dyer as the first setting for her Chalet School series, under the fictionalised name of Briesau am Tiernsee; a plaque on the wall of the village bookshop commemorates her writings.