I thought I'd add my experience about sauna Thermas as I've been going there for a few years now. I remember being very nervous the first time!
You pay the entree fee, get a key with a locker number and go change. Once you are changed you go down the stairs where the working boys will be waiting or wandering around, and on the bottom most level there's a pool and bar. Some providers will approach you, some won't. If you see someone you like just say "Hey" to them and they will most likely lead the conversation.
Clearly state what you want to happen (suck their dick, have them suck you, get fucked, fuck them, kiss or not,...) and confirm these are things he offers or not (all providers have different limits and things they offer). The standard is 50 euro for one session, no matter what the activity (usually, with some exceptions noted later on), excluding the provider's ejaculation (if you want them to ejaculate, tell them as it's extra money, usually 50 euro extra). There are "strict" tops who sometimes propose to let you fuck them for double the money (so 100 instead of 50 euro for 1 session. I suggest to not do this as they are often not good at bottoming and to search for a true versatile or bottom provider).
If kissing is important to you, ask them to demonstrate to you how they kiss during the conversation. It's forward, yes, but a good kisser will happily oblige and it can save you from disappointment as I've had providers give halfhearted pecks once the session started (when I didn't ask them to show me before).
A session lasts around 20 to 30 minutes (but you as the client should keep track. Most providers will make the session shorter if you don't). The rule of thumb is that it's 50 euro per 30 minutes. So if you were to engage a provider for one hour, it's expected you pay him 100 euro. But always confirm price and duration before starting the session. Some will (jokingly) ask for a tip beforehand, which I always politely decline.
Once you've agreed on everything, it's time to start the session. For this you have 2 options. There are free cabins on the first basement, they have a fixed bench with thin mattresses on them. Some clients find them uncomfortable, for me they work fine. I suggest using the cabins on the left of the stairs (when facing with your back to the stairs) as these have better lighting in them and there are larger cabins. Just ask the provider to get you a larger cabin and they will look for it. Most of the time the larger cabins are in use by providers who are on break (smoking and chatting).
You can also pay for a room. This is always by the hour and they come at various prices, depending on the size. All rooms have a full bed in them with linen and towels so the more expensive ones are simply larger. The comfort remains the same. The price list for the rooms is visible at the entry.
After you are done with the session some providers will take a shower with you, some won't. Then you both go the top floor (street level) where the lockers are. You then get the money from your locker. The provider will be waiting for you in the bathroom next to the entrance (you can't miss it, it will be very clear where it is) and you give them the money there. I don't know why that is the spot but it's been that spot for as long as I've gone there.
The providers don't mind it if you have your phone with you (I use it for Google translate).
If you had a great time with a provider, I suggest you buy them a drink at the bar (if they're not otherwhise engaged with another client). I find it nice chatting to the guys and getting to know them.
I totally understand one might be nervous going for the first time, but I've found that most everyone there (from the staff to the providers) are friendly and want to help you relax because happy, relaxed clients spend more money 😉
Ideal times to go are any day between 4pm and 8pm. The busiest days (with the largest number of providers, but also the most clients) are (usually) Wednesday but definitely Friday and Saturday, same time (4pm till 8pm). Outside these hours there will rarely be providers in the sauna.
Hope this helped!