This is a members' club, but you can buy one month's guest membership for 125 kr, including entrance for the first night.
There is no need to buy a full one-year membership which costs 500 kr.
I am not really into leather, SM or darkrooms, but the clientele is nice and relaxed, and the place is large and reasonably clean. I guess it comes in as just above average on an international scale. SLM Oslo is more interesting, Stockholm is said to be good too (but I haven't been there).