Around Beckenried you have a lot of options to have a swim and spend the day in the sun.
Bauen is a nice little spot to relax and swim. It has a Restaurant and a little kiosk). Bauen can be reached by car (drive trough the Seelisberg tunnel) and on the way to Bauen you can watch the
kite and wind surfers in action. You can also walk down from Seelisberg to Bauen (2 hrs) and take the boat back to Treib and up the way with the cable car.