I love that Basel is right at the boarder of France and Germany. You can literally walk across the boarder. Thus, my favorite day trips include places from both Germany and France.
I know that Alsace is a whole region (in eastern France) but anywhere you go in this area is beautiful! Most famous are Colmar and Strassbourg. They are super charming but easily get a little too crowded for my taste. So I prefer the tiny villages along the route de vins. The road winds for 170km and connects some of the most beautiful villages in Alsace. Riquewhir is usually the first choice. I personally loved Ribeauvillé and all of the castles and ruins in the area. Find out more.
Schauinsland (German for „look into the country“) is a mountain in the Black Forest, near Freiburg im Breisgau. The top of the mountain may be reached by Germany’s longest cable car. It’s a perfect location to enjoy nature and even ski during winter. On the way back you should stop in Freiburg and enjoy a nice coffee & cake or even dinner.
3 Rötteln Castle
This castle is located close to Lörrach and perfect for a little excursion. I suggest that you ride there by bike. Start in Basel by following the river Wiese until Lörrach. You will then soon see the castle up the hill to your left. Warning: the last part up the hill is quite steep. The reward is worth it though. They also have a cafe and beer garden. If you choose to go by car, free parking is available.
4 Petit Camargue Alsacienne
This is for all the bird lovers out there. The Petit Camargue Alsacienne is a nature reserve. You can walk along the marked paths and be inspired by the beauty of nature or observe the fauna from the observation stands. The area is home to 12 types of fish and 174 bird species. The best way to get there is by bike. From Basel you take direction „Huningue“ and simply follow the Canal Huningue.