4 days in Blackforest

"I also could not get a clear map of the railway route"

There are not a lot of rail routes in the Schwarzwald (here is a rail map of all of Baden-Württemberg), but towns are well connected by bus. With staying in a town like Schiltach, you'll get a Konus Karte, a pass good for all the trains and buses in the Schwarzwald.

In 2000, I spent a couple of nights in Alpirsbach, just up the Kinzig from Schiltach. It's a beautiful area. I took the train up to Freudenstadt and discovered one of the gems of the Schwarzwald. (If you go to Freudenstadt, don't get off at the Hbf in the valley and have to walk up the long hill to town. Change to one of the shuttle trains that goes up to the Stadt Bahnhof, which is only a few blocks from the large town square.)

I don't know about Triberg being too touristy, but the station is well out of town, requiring use of a bus to get into town. I was in Titisee in 1988, and it was already the epitome of touristy.

Thanks a lot !
That would be really helpful for me ! :)

Would you be willing to rent a car? I can suggest some beautiful scenic routs to drive. One includes many castles. But if you're set on a train, then I guess my advice would be pointless. It's such a beautiful area though, you will enjoy it whatever way you choose. I would personally drive it though if it's an option.

Yes, true ! Car would have been the best bet in the BlackForest but unfortunately we aren't the best of drivers ( :) ), so we will have to avail the trains and the buses as mode of transport ! :)

"I want to avoid Triberg, as I heard it would be too touristy..."

There are lots of tourist shops. The Black Forest Museum there was quite interesting - but much of it is signed in German only.

"I also could not get a clear map of the railway route - mainly got about the Offenburg to Donaueschingen route."

On the above route, the Black Forest Railway or Schwarzwaldbahn, I'd suggest Villingen, a very handsome town with relatively few tourists.

Other Black Forest train routes you might be using:
Kinzigtalbahn to Freudenstadt
Hell's Valley Railway or Höllentalbahn
Rheintalbahn (Konus card is valid north as far as Karlsruhe on the regional trains - not on high-speed trains.)

You will love this part of the Black Forest. One day wandering through Schiltach will be a pleasurable day. A number of very interesting museums are there - some are free, and the town itself is very enjoyable. This area has amazing history. You can easily spend a good part of a day in the Open Air Museum just north of Gutach - Vogtsbaurenhof. Haslach and Wolfach are also interesting places to explore. We had the freedom of a car, but as other posters have noted, there is a very good transportation system up and down those valleys.

Thanks a lot for the suggestions !
will plan accordingly ! :)