Swimming
You can swim both in the lakes of brienz and thun. the water in the lake of thun is generally warmer ~20â°c in july/august. a popular swimming area with showers, changing rooms, a restaurant, etc. is in neuhaus. a real insider-tip is the beautiful "burgseeli" in ringgenberg-goldswil. burgseeli is a nature reserve, where water temperatures can reach up to 27â°c and you can swim among ducks and water lilies. the natural lido offers a non-swimmers pool, paddling pool, childrenâ´s playground, restaurant, changing rooms, showers, etc.
Hiking
There are plenty of great hikes in the interlaken area. popular near-by hikes include harder mountain mountain train 5 min. from interlaken ost station and schynige platte mountain train from wilderswil.
Sailing
Lake thun is quite popular for sailing. you can rent sail boats and book classes in neuhaus.
Walks
Take a walk along the shores of lake of thun thunersee or lake of brienz brienzersee. a nice, ~2h walk goes from west train station to "neuhaus". it takes you along the aare river and through the small but popular nature reserve neuhaus at the lake of thun. from neuhaus you can take a bus or boat back to interlaken.
Take a boat trip
Boats traveling the Thunersee leave from Interlaken West. If you go all the way to Thun, you will see many cute towns and beautiful buildings/small castles on your way Spiez, Oberhofen. There is also a castle in Thun. Boats traveling the Brienzersee leave from Interlaken Ost. The water in the Brienzersee is a beautiful shade of turquoise. The boat is free if you have the Swiss rail pass.
Skydiving in Interlaken
Funrental interlaken offers helicopter or plane jumps including 4000 meters in 40 seconds freefall jumps.
Biking
Take an awesome mountainbike ride around the lake of brienz 4 hours and visit the giessbach waterfalls on the way. alternatively, visit lauterbrunnen by bike ~2 hours one-wayand look inside the trã¼mmelbach-waterfalls trã¼mmelbachfã¤lle.