Mirrormere or Kheled-zâram in Khuzdul was the lake 'Durin the Deathless' looked into & saw a crown of stars above his head. A reflection of the stars even though it was daytime. Taking the crown as a sign Durin founded Khazad-dûm under the mountains that fed the Mirrormere.

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"He stooped and looked in Mirrormere,
And saw a crown of stars appear,
As gems upon a silver thread,
Above the shadow of his head."

day 26 : stars

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