Thac Ba Lake is a beautiful man-made lake located in Yen Bai province. It is surrounded by lush green mountains and offers breathtaking views. You can take a boat ride on the lake and enjoy the tranquility of the surroundings. There are also several islands in the lake that you can explore. Don't forget to visit the Thac Ba Temple, which is located on one of the islands. It is a sacred place for the local people and offers a glimpse into their culture and traditions.