Been to the sauna a few times the past week and even though there were few remarkable sightings, I thought I'd share my "rule book" - that's what I do to make sure I'll make the best of it, maybe it's benefitial to some of those who'll try it in 2022
Rule 1: Don't go there just to peep. You'll be there for a long time and spend a lot of money and you will be disappointed if you're unable to enjoy the sauna for its original purpose. Also, you'll look weird (see rule 2)
Rule 2: Try to understand the customs and procedures and adhere to them. Otherwise, you will stick out like a sore thumb and will make others, especially women uncomfortable. While they will rarely complain about or to you, they will leave or cover up (short-term damage) and/or will be less likely to be there in the future (long-term damage).
Rule 3: Don't stare. It will make them uncomfortable (see rule 2). Everybody, including the women, expects to watch and be watched to a certain degree but staring is strongly frowned upon.
Rule 4: Never ever follow someone around, they will notice. Instead, try to anticipate the next move of somebody you're interested in and be there before them. See the next rules for elaboration.
Rule 5: Sauna cabins are the worst place to voyeur someone. They are usually dimly lit and usually women will sit in a way that you will only see them topless at best and wrap in a towel the second they get up. Also, often people will leave a cabin when a stranger enters. Aufguss sessions are exempt from this rule as they are usually tightly packed and people expect others to join.
Rule 6: Showers are great. Everbody is expected to shower after each sauna session and you can't do that wrapped in a towel. Sometimes, there are gender-separated showers close to the changing rooms, but most women will use the mixed ones that are closer to the sauna cabins. Timing is essential for this to work though as you will look weird if you hang out in or next to the showers for too long. A great opportunity is the end of an aufguss session as there will be lots of people heading to the shower at once and the times are announced in advance. When you're very very lucky, you can grab a desk chair or similar with a view into the shower area.
Rule 7: Pools are even better and your only opportunity to see those women that head to the gender-separated showers. The better saunas will have lavish in- and outdoor pools and virtually nobody will pass on the opportunity of using them. In most layouts, there will be a stair leading into the pool and there will be hooks for your robe a few meters away, so they will have to walk for quite a bit from placing their robe until submerging into the pool fully naked without any opportunity to cover themselves. Just pick yourself a spot in the pool where you have a good view of this and enjoy. Especially when you're with a friend or, even better, your wife you will be able to stay there for a long time without looking weird.
Following these simple rules, I tend to enjoy my visits in their own right and see lots of tits and pussies every time. Your mileage will vary of course, I you have suggestions were I can improve, I'd love to hear them