"Have a biscuit, Potter."
-- Minerva McGonagall (OP12)
McGongall’s office is decorated with a lot of tartan plaid. She keeps a tin of biscuits on her desk and usually, the Quidditch Cup on her shelf. Her office has a fireplace with a mantelpiece, and the entrance is evidently within easy walking distance of Myrtle’s bathroom (CS18). The fireplace can be connected to the Floo Network when necessary (HBP18). At least one of her windows overlooks the Quidditch pitch (PA9).
Some of the corridors along the route from her office to the entrance to Gryffindor Tower have windows overlooking Hagrid’s cabin (HBP18). To get from the DADA classroom to McGonagall’s office, take a corridor from the DADA classroom to the nearest flight of stairs leading down; McGonagall’s door is on the left (OP12). It is here where Harry and the other fifth-year Gryffindors go for career advice.