Medusa is a dangerous monster with her own level, which is somewhere in the main Dungeons of Doom, but below the level that contains the magic portal to the Quest. Beware; as in Greek mythology, her gaze can turn people to stone. Additionally, eating the corpse of Medusa is a similarly bad idea that will also turn you to stone.
Medusa will never be left in a bones file. However, her statue will; this is bug C342-54. As this will not prevent generation of an ordinary Medusa in the game loading the bones until the statue is unstoned, this can be used to have two or more Medusas in a single game.
Any corpses of unique monsters (including Medusa) can be left in bones files, allowing you to use undead turning to get multiple unique monsters.
Reaching her island
The difficult thing about reaching Medusa is crossing the water full of sea monsters. Levitation or water walking boots are the most common ways to cross the water. Using a wand of cold, a frost horn or the cone of cold spell to freeze a path across the water is another option, as is filling the water with boulders, or some means of jumping.
If you are trying to reach the island with boulders, you can push them to the stairs of the previous level and throw items to make them roll down. Alternatively, you can read preferably uncursed scrolls of earth if not enough boulders are available. 8 boulders are needed for the first version and 16 for the second; this can be reduced to 7 and 14 respectively if you are willing to jump into water and crawl out.
If crossing the water is not an option, you may also opt to dig a hole to the next level and then come back up by using the staircase. The stairs to the next level are in the same room as Medusa, so make sure that you are ready for her before going up the stairs!
The best way to avoid turning to stone is to have reflection; she will look at you, see her reflection, and turn to stone. (This makes her different from the Greek myth, or else Perseus could not have looked in his mirror to defeat her.) This can also be achieved by applying a mirror on her. Otherwise, you may blind yourself, or polymorph into a stoning-resistant creature, or you may rely on the speed system to kill her in one turn, e.g. with a spell or wand of death. Don't rely on the sleep spell to neutralize her gaze. As of NetHack 3.6.0, hallucination will protect against all gaze attacks 75% of the time, but this shouldn't be relied upon.
You lose pacifist conduct if you reflect Medusa's gaze to kill her. Becoming invisible will protect her from her own (reflected) gaze. Pacifists may find it useful either to simply blind her and let pets deal with her "peacefully", or to blind yourself and give Medusa some powerful attack wands so she can kill herself with her own rebound.
Sometimes Medusa can escape to the upstairs, and/or up to the previous level. She can also escape downstairs. So if you lost track of her (i.e. entered blind and then she disappeared from the telepathy map but you don't see a corpse), beware of her around her lair and on the levels immediately above and below.
Medusa first appears in NetHack 2.2a.
Her lair first appears in NetHack 3.1.0. Before that version, she appeared in an ordinary room-type level. It seems likely that many an adventurer met an untimely end from not knowing he would soon see Medusa. NetHack 3.0.0 adds a number of statues to her room, but this is an ambiguous clue. The use of telepathy or a potion of monster detection is advisable.
Medusa, one of the three Gorgons or Graeae, is the only one
of her sisters to have assumed mortal form and inhabited the
When Perseus was grown up Polydectes sent him to attempt the
conquest of Medusa, a terrible monster who had laid waste the
country. She was once a beautiful maiden whose hair was her
chief glory, but as she dared to vie in beauty with Minerva,
the goddess deprived her of her charms and changed her
beautiful ringlets into hissing serpents. She became a cruel
monster of so frightful an aspect that no living thing could
behold her without being turned into stone. All around the
cavern where she dwelt might be seen the stony figures of men
and animals which had chanced to catch a glimpse of her and
had been petrified with the sight. Perseus, favoured by
Minerva and Mercury, the former of whom lent him her shield
and the latter his winged shoes, approached Medusa while she
slept and taking care not to look directly at her, but guided
by her image reflected in the bright shield which he bore, he
cut off her head and gave it to Minerva, who fixed it in the
middle of her Aegis.
In UnNetHack, hallucination protects you from the stoning gaze.