Only read on if you're too lazy to find the disco room for yourself  :) ....

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Standing in the main hall, look at the water pool in front of the large windows, turn to your left and head into the office section with the lights on. 

Go into the office on your 2nd right, by the plant, with the picture of the house from my previous map 'DayBreak' hanging on the wall above the sofa inside it. 

Stand in the centre of the rug in front of the picture and shoot the house. You will drop into the disco.

CAUTION

Dropping AI officers down the hatch can be fun, but can also cause the game to crash.