I visited the Roman Museum in Aalen which is east of Stuttgart along B29 road. It is a museum built at the site of a roman cavalry fort along the Limes. Actual ruins of the fort outside. Several other places along the Limes i identified and preserved or rebuilt. There is also a Trail along at least parts of the Limes in Germany, look for "Limeswanderweg" in your search programme.
As Limes mainly was built of wood, it is not likely much could survive up to now. They have rebuilt tower for guardians some 10 km east of Aalen and in the same areas are some other sites to look at.