Wikipedia
Bilskirnir
Bilskírnir ( Old Norse "bright-crack" (poetic)) is the hall of the god Thor or Þórr in Norse mythology. Here he lives with his wife Sif and their children. According to Grímnismál, the hall is the greatest of buildings ever made and located in Þrúðvangar In Grímnismál it states: "enn hǫll hans heitir Bilskírnir: í þeim sal eru fimm hundruð gólfa ok fjórir tigir" - (Five hundred floors and forty tens) NB "hundred" in Old Norse actually meant 120, as that was the basic counting system. Also 'gólfa' actually means floors not rooms. Therefore, one translation would be that Bilskírnir has 640 floors.