I used to go regularly for about 3 years. I have to say, it really was amazing and the times I had there, wow. Not all clubs are the same, but this was a decent group of people in a large nice country house.
Ages varied but most were the early 20's to 40's bracket. Some of the girls which went, wow, stunning. I always went as a single guy and once you earn the respect and trust of the people there, then your invited all the time. I got invited into threesomes, foursomes, mass orgies on giant beds, bukkake sessions, bit of submission with the stunning blonde who hosted the parties (was a bit of a dom), I made friends with some of the couples who went there and got invited to their private parties in their homes, even ended up in a short relationship with one of the girls who went there.
Yeah, was amazing and some of the stuff I saw and joined in with will always put a smile on my face and a bulge in my pocket.
My advice to you - dont go expecting something, first time you never do get up to anything as people are weary of you. Take lots of condoms. Dont get drunk. Be respectful, and remember no means no. Get to know the people there, make friends and over time it will all be worth it.