Well, that most certainly not really in between these 2 Swiss places.

You hit 1 right-it has hourly RE trains-doubledeck and you can even spot-if quick-the largest cuckoo clock in the world from it. The next -also quite good-line runs east from Freiburg and joins up with this line around Donaueschingen-it passes some famous cliff. Somehow I recall there are-again-works for a,longer period along that line, but I have to check all details, you can also do yourself via the bahn.de planner.

Note that IF you stay for a day or 2 in the Black Forest area (NOT the main city Freiburg) most HTLs will give you a Konuspass which is valid during stay for unlimited free transportation-also bus-in this area. it may be worth it. Google Konuspass and follow the links.