Enjoy one of the most beautiful lakes in the Dolomites, Lago di Braies! I can 100% recommend to go there, the views are just amazing and if you dare, take a swim in the clear water (or rent a boat if the water is too cold ;-)).
I recommend to go to Lago di Braies early in the morning or in the late afternoon. This, especially when you go in high season (summer). We went in June, arrived around 3PM and that was perfect. Another recommendation I can give you is to walk around the lake. It can seem a very touristic place when you arrive, but I guarantee not everyone is walking around the lake so it gets less busy once you're walking around the lake!