Almost everything is legal in Achamoth when it comes to entertainment, and there is not much government oversight in the way anything is run. This means that everything you've described is both present and largely unregulated, and it doesn't need to be underground on account of how permissive Achamite law is. Brothels, drugs, and even bloodsport are all fair game... technically, participants in brothels and bloodsports must be willing but that 'consent' can be pretty nebulous. 'Extreme' bloodsport is generally hush hush (those that are particularly graphic and unpleasant, or basically torture) and behind closed doors mostly just to avoid causing a fuss.

The one thing there is official rulings on, straight from the Regent, is the enforcement of 'age of consent' and laws against child abuse. Children are generally not allowed to participate in those skeevier activities and there is a cultural expectation for people to raise their children properly, though this still goes wrong fairly frequently. It's just one of the things that is actually punished. Adults, however, have fewer innate protections.

Achamoth's hedonistic atmosphere means there is plenty of dubious sexual activity going on, but on an OOC level we would ask that characters who are younger than 18 refrain from participating in it. This is largely for the comfort of other players (and the mods themselves.)