The Oracle is located between levels 5 and 9 of the Dungeons of Doom.
The Oracle level is eligible to leave bones files. Monster creation on this level is biased towards neutral monsters.
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Legend
There are five rooms to the sides of the above area, containing the stairs (in separate rooms), five random monsters, three random traps, and six random objects; they are linked to each other and to the mapped room by corridors. The Oracle is at the centre of the 3*3 room ("Delphi"), amid the fountains; Delphi has a random empty doorway in one wall. The marked statues are two of forest centaurs (NW and SE), two of mountain centaurs (NE and SW), and four of plains centaurs (N, W, S, and E). There are two random monsters in the area surrounding Delphi.
#chatting to the Oracle can get you advice; the charge for a minor oracularity (from the true rumours file) is 50 zorkmids, for a major oracularity (specific, if highly cryptic, information) is 500 + (50*XL); this exercises wisdom, and the first of each type gives a small amount of experience.