Donnybrook is a district in Dublin, Ireland, that was once the site of Donnybrook Fair, a fair held starting from King John's reign that was infamous for drunkenness and violent behavior, which gave rise to the term, "donnybrook", meaning a brawl or fracas. The fair was banned in 1855.
In the northeast of the level, the metallic corridor connecting to the room with the shack has a set of panels in the south placed lower than the rest. This is a secret door (sector 267) leading to a partial invisibility and a lift with a medikit on it, leading up to a sergeant.
The space where the partial invisibility sits (sector 269) is also counted as secret.
Moving northwards from the blue armor raises (Linedef 731, Type 130 - W1 Floor Raise to Next Higher Floor (fast), Tag 83) a barrier (sector 133) behind the player that can temporarily be lowered using the switch (Linedef 639, Type 123 - SR Lift Lower Wait Raise (fast), Tag 83) to the north. After leaving this compartment (with a stimpack in its north), it becomes inaccessible. There is another switch (Linedef 1125, Type 123 - SR Lift Lower Wait Raise (fast), Tag 83) that is supposed to open the barrier, but it is blocked by sector 217 that cannot be opened since it is missing a tag.