The Corona Protection Ordinance NRW applies, which can be simply summarized as the AHA and 3G rule. For the museum visit the AHA rule applies, i.e.: Keep your distance (at least 1.5 meters), observe hygiene rules (cough and sneeze into your elbow and wash your hands thoroughly) and wear a mask in everyday life.
If you take part in guided tours or workshops, the 3G rule also applies: vaccinated, recovered, tested. Please have proof of complete vaccination, recovery, or a negative result no older than 48 hours available.