The Rhaetian Railway leaves Chur to Arosa and back at hourly intervals. Take the local bus from the train station Arosa towards the Untersee lake.
It is best to park the car at the parking garage Ochsenbühl. Right in front of the entrance to the lido is a parking lot with a few parking spots.
At the Ochsenbühl parking garage. There is a limited number of parking spots at the Untersee lake.