Well it is a popular time to be travelling around Europe. You are in a good region to find plenty of tourist attractions.
One of the biggest attractions in the area is the Neuschwanstein Castle. It is pretty spectacular.
If you want to do more low key stuff, you will be in some of the best brewing country in the world so touring a brewery would be a thing to do
If you can and want to travel a bit more. One thing that is very close is Slovenia and a little town called Bled. The gorge there is fantastic in the summer and the lake is beautiful aswell almost 10 years ago
Duisburg might be hosting the Berlin Love Parade at the end of July (Berlin doesn't want to host them anymore...), that could be interesting!
I would definitely recommend getting up to Berlin, which is one of my favourite European cities. Neuss, Dusseldorf and Cologne are also nice places to visit within Germany. Great time of year to be travelling - I suggest hiring a bike and cycling round some of the cities, thats one of the easiest (and fun!) ways to get around. almost 10 years ago