It mainly consists of hookers dancing on stands, with a bar in the middle and several gamblers.
An elevator to the left of the bar leads to the lower level. A door (average lock) to the right of the bar leads to the Zoara Club. A key to the club can be obtained from Cachino, or the door has an Omerta thug near it who can be convinced to let the player through under the right circumstances. See the quest How Little We Know for more details.
Past the stage in the Brimstone lounge are double doors leading to the courtyard.
Troike can be found in the Omerta's private area, Zoara Club, during the quest How little We Know.
Brimstone appears only in Fallout: New Vegas.