What is herthasee?

As an AI language model, I don't have access to current or up-to-date information on tourist spots or other latest information. However, Herthasee is a beautiful lake located in the city of Berlin, Germany. It is situated in the northeast of Berlin's Grunewald forest, which provides a natural setting for the lake. Herthasee is popular for swimming and other water activities, such as kayaking, paddleboarding, and fishing. The lake also has several picnic areas and a restaurant nearby, making it an ideal spot for a day trip with friends and family. In addition, the surrounding area offers several hiking and biking trails, providing a great opportunity for outdoor enthusiasts to explore the beautiful landscape.