The northwest chamber in the large Place of the Hearth was called the Chamber of the Place of the Hearth. From this chamber, the priests would descend to the "winding passage" - a spiral staircase that led to the Immersion Chamber. In the Immersion Chamber, the priests would immerse themselves in a ritual bath before performing their service in the Mikdash. There was also a lavatory in the Immersion Chamber referred to as "the seat of honor" for reasons of modesty. (Source: Tamid 1:1). 
Dimensions
Contents:   Part I,    Part II,    Part III,    Part IV,    Part V,    Part VI,    Part VII