This is one of my travel essays.
If you head north out of Wiesbaden....about an hour's drive to the northwest is Koblenz. There's probably enough in the town to spend an entire weekend (a full Saturday and most of Sunday) there.
In 1897, roughly nine years after Kaiser Wilhelm I died, the locals completed this statue to the guy. It's best to say that Wilhelm I was fairly admired around the country (perhaps more so than his grandson Wilhelm II).
I'd allocate an hour to walk around the park and admire the statue work.
If you look across the river, there is the old fortress. You will have to board a cable-car (couple of Euro) to get across to the hilltop. For the fortress, I would allocate a minimum of four hours. If you are the historian type....maybe eight hours. There is a cafe on the very top, along with two or three coffee, soda and beer operations as well.
I should note that this is a pretty large facility. If you've come with a couple of kids.....you will find it impossible to manage them or find them. Yes, you can literally get lost in this fortress. So you might want to establish some rules or hand the brighter of the kids a map.
The French, Napoleon's crew, came and destroyed the original fortress there in 1801.
I should note that there's been some type of fortress on this hill since 900 BC, or at least the locals believe that. The Romans eventually arrived and added to it, and after them....the Catholic Church.
Around 1815, this region of Germany became part of Prussia. They worked from 1817 to 1828 to build what you see today. The idea was....it was to be a place that no French Army would ever take on again. This was true until 1945, when the French Army took over the region. Two years later, they released the fort to the local state. It went through various stages, but today is a major tourist attraction for the local area.
I should note, it's not a free deal to the fortress.....11.80 Euro for an adult, and around 5.50 for a kid.
Between the old city area, the walk around the river, the Ecke, and the fortress.....provided you arrive by Friday evening....you will have enough to check out for an entire weekend. I would also recommend any of the dozen-odd restaurants along the river near the Kaiser statue for lunch or dinner. Naturally, all of this means walking....a fair distance over a weekend.
So, if you were looking for some four-star history theme weekend.....Koblenz would be a great fit.