The Alb valley has lots of options for easy to medium outdoor activities on foot and by bicycle. The forests have a dense network of hiking trails, all well marked and signposted. You can start walking everywhere along the valley and select a short or long tour just as you like.
The tram network allows one way hiking tours over the hills from one valley to the next. Arriving on the Alb valley tram S 1 you could either hike South to the Murg valley and take the S 41 back, or North to Ittersbach or Langensteinbach and return on the S 11.
For an easy bike tour, there is a bike trail along the whole valley. Bikes can be transported for free (on weekdays after 9 a.m., on weekends all day) on the trams, so you can take your bike up to Herrenalb and comfortably cycle back downhill along the river. Mountain bikers and hardcore cyclists will find roads and marked mountainbike trails up and down as many hills as they want.
The house next to the bridge is inhabited by the sculptor Detlef Dwarnicak (not that I had ever heard of him before but that's what the sign outside the house says...) This guy does wooden sculptures of all kinds in various styles. If you walk past, have a look into the garden. There is a totem pole, a group of chickens, an owl, a bearded spirit with mushrooms, frog and snail...
I wonder about the hooded figure in front of the house, it makes me think of a dementor.
The name of the village indicates its origins: Marxzell = "Marci cella". A cella is a dependance of a monastery, with two or three monks who take care of a parish church and its community. Saint Marcus, Mark the Evangelist, indicates a relationship with Reichenau abbey in the early ages. Later on Marxzell was connected with Herrenalb.
The catholic parish church is still dedicated to St Mark. It is the oldest parish church in the Alb valley. The steeple remained of the 14th century church, the nave was substituted by a new and larger one in 1782.
The chapel inside the steeple contains the tombstones of the last nuns of Frauenalb who died in the early 19th century when their convent had already been closed down.
I would have liked to see the interior but the church was closed, and I could not find any hints about regular opening hours.
The whole length of the Alb valley up to Bad Herrenalb is well connected to Karlsruhe's tram network. The line S 1 runs from Bad Herrenalb via Ettlingen to Karlsruhe, passes both Karlsruhe central station and the city centre and continues to the northern suburbs. Important stops are "Marxzell" for the car museum and the village, and "Frauenalb-Spielberg" for the ruins of the convent. A visit to Marxzell can well be combined with Bad Herrenalb.
When coming from Karlsruhe, check carefully because the S 1 runs every 10 minutes in the city, but not all of them do the whole way, many end in Ettlingen. Two trams per hour (daytime hours on weekdays) continue to Bad Herrenalb, the interval is 20 and 40 minutes alternating. In the evening and on weekends there is one tram per hour. Have a look at the timetable before starting your trip to avoid long waiting periods (lesson learned the hard way). And don't confuse the S 1 and S 11, the S 11 leaves the Alb valley in Busenbach and continues to Ittersbach, in other words, wrong way.
Download of S 1 timetable
Fares: A single ticket from Karlsruhe to Marxzell or back (5 zones) is 3.70 € (same zone as Bad Herrenalb).
Groups up to five people travel cheapest with the Regioplus ticket for 13.50 € which is valid for 24 hours of unlimited travel in the whole KVV area.
Marxzell is a small village but the traffic running through it is by no means village-like. The main road which runs past the train station and the car museum is a Bundesstraße, a major country road, with rather heavy traffic. Many drivers don't slow down as they should be. The zebra crossing in front of the museum is meant to provide safety for pedestrians but - hm, I'm not so sure how far you can really trust car drivers. Better look left and right twice.