Hamburg has a very good public transport system including buses, trams, S-Bahn, and regional trains. Your conference badge includes a public transport ticket for the duration of #CHI2023. Pick up your badge and you are good to go in the area A-F (see this map) – which is the complete city and some of the neighboring regions. Taking public transport is easy and a sustainable way to get around. You can find public transport options in Google Maps, using the HVV App or webpage (https://www.hvv.de/en).
On Sunday (April 23rd, first day of CHI2023) is also the Hamburg marathon – probably too late to start training or register, but it is good to plan a bit more time for getting to the conference center as some roads are closed, see http://mhv-maps.de/Marathon/Verkehr/index.html
Hamburg is also very walkable, there are rental bikes and rental scooters.