A (family) trip to the Fortuna Mine, only 11 km away, with the adjoining Field and Mine Railway Museum is definitely worth it. The former iron ore mine is now one of the very few visitor mines that can be visited during very informative mine tours.
Tip: If you present an admission ticket (normal price) from Braunfels Castle at the Fortuna Mine ticket office, you will receive a discount on the normal entrance price – and vice versa (one-off, double discounts are excluded).
You can find more information here » https://www.grube-fortuna.de