I'm going to be spending 3 days in Düsseldorf, for a mixture of work and holiday, so I'm going to need to do a fair bit of travelling around the city to get to both meetings and sightseeing/museums/etc.
Are there any public transport tickets I could get which would cover me for the three days for a number of journeys, to avoid needing to buy individual tickets each trip? And if so, is it possible to get one that covers both the city centre area and the trip to/from the airport? Or would I be better off getting a return ticket from the airport into town, and then some sort of multi-trip/multi-day ticket once I'm there?