Black Forest

Hard to imagine a worse choice

Kehl is not a high-brow town but OK as a travel base, and sometimes you can find rooms there when Gengenbach and Strasbourg are full (or too expensive.) From Kehl you are of course near Strasbourg but also only about 1 hour by train from the quite terrific Vogtsbauernhof open-air museum in Gutach; use Gutach Freilichtmuseum when you search for a train stop.

Gengenbach is closer yet, about 30 minutes.
https://www.pfeffermuehle-gengenbach.de/files/gengenbach-innenstadt.jpg
https://www.reiseerlebnisfuehrer.de/wp-content/uploads/2014/04/Gengenbach-Engelgasse.jpg
http://www.gengenbach.info/

A little thing called the Europass 24h can get you to Gutach and Gengenbach. Buy it at a ticket machine in Kehl, day pass for one is €9.30, €14 for 2, and some kids are included. Hope your French or German is OK...
https://www.ortenaulinie.de/site/OrtenaulinieRoot/get/documents_E55738180/ortenaulinie/Dateien/pdf/tgo_europass-folder_2016_web.pdf

Have you actually booked and paid for your place in Kehl? It is a pretty busy and not particularly attractive place, despite the usefulness of the tram (and train) into Strasbourg.

I'd have picked a place further along the train line like Gengenbach, where you can easily get out into the countryside. For trips into the Black Forest you can go anywhere the Black Forest train goes. Have a look at the wiki for the railway and they talk about the different towns along the line. Loads to do. What do you want to do? Hike? Summer toboggan? Toilet museum (yes, really)? Clock museum? Stork hunt? Medieval city walls? Model train layout (huge, one of the best in the world)? Train ride through the valleys and tunnels? Lake and beach?

If you stay in the Black Forest (with a few exceptions) you get a free KONUS card which gives free travel on slow trains and buses all over the area. Does your place in Kehl offer you that? (not snarky, curious).

Agree with Russ & Nigel. Gengenbach is a great little "dorf" to stay for several days and use as a launching point into the Schwarzwald. We enjoyed the Hotel Sonne. For a day trip, my wife & I used the Kronus card and took a bus (slower) through many of the cute towns into central Schwarzwald, ending at the town of Triberg. At the end of the day we returned back to Gengenbach on the train (much faster).

I have a room reserved can cancel anytime (booking.com) I chose Kehl because 1) Strassbourg for a day is key, 2) I can train thru the Black Forest for a day reasonably, and twice I have driven from Alsace thru Gutach and Triberg to Ulm. Just want my travel partner to see the black forest. 3) I can't see any hotels on booking available for a better rate.

The train to Strasbourg through Kehl originates in Offenburg, also not an exciting town, but a little bigger for a base. Offenburg is also a terminus for the train to Gengenbach and the Black Forest Railroad.

Sounds like the major emphasis for the trip is on Strasbourg with a small amount of time devoted to the Schwarzwald. Why not simply stay in Strasbourg and forgoe any journey into northern/central Schwarzwald. Instead, you could also journey from Strassbourg to Colmar and sample the local wines/cheeses. From Colmar you could easily venture into southern Black Forest, such as Freiburg where you could catch a Bundesliga match with SC Freiburg.

Are there any b and b's in offenburg...Or recommeded gasthauses????

Are there any b and b's in offenburg...Or recommeded gasthauses????

In Gengenbach, Schwarzwald Villa (small B&B, walking distance to central town and train station.)