Hiking to the castle
You may drive up to the castle or take one of the small buses,leaving at the old townhall or you may take a walk uphill on your own.
There are several small hicking-paths leading up the hill and within 20-30 minutes you will be at the castle, depending which path you take.
Along the way you will have plenty of great views on the city, and maybe you drive up by bus and take the walk down, like I did myself. No special hiking shoes are required, but walking in high heels is certainly not a good idea.
Especially in autumn the path might be slippery at some places.

Passau playground
Relaxing on the upper deck of Swiss Crystal
Ms. Furth & Larigot at the console
The Jesuit church / Jesuitenkirche of St.Michael