I visited Zeche Zollverein in September. Since there are so many detailed reviews on content etc. I focus on the "post-corona" update and some organizational hints.

Access: Very easy from downtown Essen by public transport in 24 minutes, and even from Düsseldorf main station it only takes less than an hour. But also by car it is easy and parking is available. Nearest bus/tram stations are: „Zollverein“ (Tram 107), „Zollverein-Nord“ (Tram 107, Bus 170, Bus 183 oder Train RB32) or bus stations „Kokerei Zollverein“ or  „Kohlenwäsche“ (Bus 183).

The area is accessible without entrance fees, but it makes much more sense to take a guided tour (charged, but not too expensive). Also, the different museums (e.g. the very famous Red Dot Design Museum) do cost money. There are several tours available from 30 min to 2 hours. Some tours include reports from people who really worked there. Also for people who cannot or don´t want to walk, there are bus tours around the huge area. There are no Corona measures neccessary anymore.