Places to visit in Düsseldorf

Hi,

For the ones living in Düsseldorf, what would you suggest to discover the region?

When you have friends or family visiting you, where do you go with them? What are the must-see places in Düsseldorf, the tourist sites?

How to visit the region in an original way? Any unusual or unknown place to recommend?

What would you suggest for a couple of days of for a week of holidays in Düsseldorf?

Thank you in advance for participating ;)

Julie