Roscoe below has given an accurate summary of SBN, but I'll give a more recent version.
If you go to SBN make sure to go between about 14:30 and 18:00 as those are the peak hours. Most of the clientele are between 36 and 60 with the odd few guys that are in their twenties. It can get very full on with group activities going on in most corners. Definitely be careful on the stairs as they're prone to be slippery. I can guarantee that you will get groped even if you don't want it, but a simple hand movement will usually deter them. If someone persists then the security are more than happy to have them removed. Lube and condoms are provided. Great fun.