The only way to reach Arosa is from Chur: take the hourly narrow-gauge train that leaves from in front of the train station (Sfr15.40, one hour). It's a winding journey chugging past mountains, pine trees, streams and bridges. The train crosses the oldest steel-and-concrete rail bridge ever built. At 62m high, it's a dizzying engineering feat, completed in 1914.
By car, it's a winding 30km drive from Chur that will take 40 minutes with good road conditions.