Overseeing the valley of Schirmeck, the castle, built for the Bishop of Strasbourg in the 13th century, is a short walk and climb from the town centre. As it was designed to protect a corner of the territory, that's apparently where we get the term: Schirm'eck. It was defeated by the Swedish during the Thirty-Years War, with some of the stone from the ruins being used to build other structures, such as the church.
Today, there's obviously not much of it left, though a square tower was restored and houses a small museum (closed when I visited). The Yoshi art was probably not part of the original episcopal aesthetic...
In the woods above Neuviller-la-Roche and Natzviller are the Serva Falls. While not the largest we've covered, they are still sizeable, with the river flowing over rocks a small distance either side of the main fall.
It's a good hiking destination from Rothau or even Schirmeck station, depending on how far you're prepared to walk. I started in Rothau, had lunch by the falls, down the river back to Rothau, and wound up adding a walk in the valley to Schirmeck while waiting for the next train...
A good hike I'd like to do is 2-day, 30-km walk from Rothau up past the falls to Champ du Feu, the highest point in Bas-Rhin, and on to the plains at Barr. But I wouldn't want to do it alone.