It should be noted that this road is ALWAYS CLOSED DURING WEEKENDS in the Glarus part, from the Klontaler see to the border of the Kanton. At weekends the Pragelpass can be reached from the Schwyz side.
I drove it (on a Monday) from Schwyz to Glarus, and I found the scenery amazing when driving down to the Klontalersee.
Not a road for fast cornering emotions, too narrow with blind corners. Still an unparalleled experience for tourers that love scenery and environment.
It looked like a promising route; I planned to ride it from Glarus to Schwyz after doing the Klausenpass eastwards, but the road was closed just past the Klontalersee (have no idea why). Still, the Klontalersee was worth the trip.
This route runs approximately parallel and to the north of the Klausenpass. It would be a nice return trip back to Glarus or Schwyz if you took the Klausenpass one direction and this trip in the opposite direction. This is a very narrow road in the section through the mountains. To get to the beginning of this road, take the Bahnhofstrasse east out of Schwyz, left on Scheidgasse, right on Strehlgasse, then the road turns in a U-turn and becomes Grundstrasse. If you follow Grundstrasse for about 10 km, you find it turns into Kustnau, and then Hauptstrasse as it enters Hinterthal. At the east end of Hinterthal, jump over the bridge onto Pragelstrasse, and follow this road for about 30 km. At some points, this road goes down to one lane, and I have heard that the pass closes on the weekend except to bicycles and foot traffic. HOWEVER. If you can manage to navigate this road, there is a spectacular lake called the Klontalersee towards the Glarus end of the route. It is an amazing emerald green color with several spectacular falls. At the east end of the lake turn left onto Klontalstasse, or go straight on around the lake. Both roads dump you back down the hill into Glarus. This sia very pleasant ride, best accomplished before dusk and on a sunny day. I have posted photos on my travel log... www.travel-switzerland.net. I did not see any police when I rode this trip, but I recommend caution, as it can be very narrow inplaces with blind turns. Enjoy!