"...it was a very beautiful, circular room, lined with pictures of previous headmasters and headmistresses of Hogwarts, all of whom were fast asleep, their chests rising and falling gently."

Albus Dumbledore's Office

The entrance to Dumbledore's office at Hogwarts is behind a statue of a gargoyle. When given the proper password, the gargoyle will leap aside, and the wall behind it will split in two to reveal a spiral stone staircase that moves like an escalator Dumbledore's password for the gargoyle always seems to have been the name of a sweet, and to have been known to the various staff members though not to the student body at large. However, the office can be sealed so that none can enter save the rightful Headmaster or Headmistress, and also can be sealed so that someone already inside cannot leave without the Head's permission.

Once in the door, visitors ride on a spiral stone staircase that moves slowly upward as the gargoyle's entrance closes behind them. The staircase leads to a highly polished oak door with a brass knocker in the shape of a griffin. The door is not sound-proof; a visitor standing on the staircase can hear anyone speaking in the room inside, although not necessarily distinctly unless the speakers' voices are raised.

The oak door opens into a large and beautiful circular room with windows, at least one of which faces east with a view of some of the mountains surrounding the castle. The windows also afford a view of the Quidditch pitch. Although the windows had curtains back in Armando Dippet's day, Dumbledore does not seem to have ever been in the habit of drawing them, even on snowy winter days or at night.

By day the office is sunlit, while at night it is illuminated by candlelight and lamplight. The walls of the office are covered with portraits of previous Headmasters and Headmistresses. The wall immediately behind the Headmaster's desk has a shelf holding the Sorting Hat. Gryffindor's sword is kept in a glass case beside the Sorting Hat. Another wall of the office holds a fireplace that can be connected to the Floo Network when needed.

The Headmaster's desk is an enormous, claw-footed affair that apparently goes with the room, since it was in use in (former headmaster) Armando Dippet's day. The surface is highly polished, though naturally it is sometimes covered with papers. Dumbledore also kept a silver ink pot with a handsome scarlet quill (possibly a phoenix feather) on the desk. The desk faces the door leading up from the gargoyle; a visitor standing with his back to the Headmaster's chair (which is particularly high-backed) will find himself or herself staring out at the Quidditch pitch.

In Dumbledore's day (although not in Armando Dippet's), the office contained a number of spindle-legged tables supporting various "curious silver instruments", the function of which Harry did not know as of his sixth year, that seem to whir and emit little puffs of smoke day and night regardless of whether the Headmaster was actively consulting them, present, or even in residence.

Behind the door in Dumbledore's day (though again, not in Armando Dippet's) a golden perch for Fawkes stood. Beside the perch was a black cabinet which Dumbledore at one time used as a drinks cabinet, although by Harry's time at Hogwarts the Headmaster kept a Pensieve there instead.

Source: HP-Lexicon.

Passwords (Book/Chapter)

Acid Pops (HBP9, HBP10)
Cockroach Cluster (GF29)
Fizzing Whizbee (OP22)
Lemon Drop (CS11, US Edition)
Sherbet Lemon (CS11, UK Edition)