For a concept that appears so frequently throughout the Bible, the "Upper Room" has so many shifting meanings and contexts, that it is difficult to pin down what it really is. First mentioned in the Old Testament, it is thought of as having particular significance as a sacred site. A space for things holy. In the Book of Chronicles, David instructs his son Solomon to build the Temple of God.
"David gave Solomon his son the plan of the vestibule of the temple, and of its houses, its treasuries, its upper rooms, and its inner chambers, and of the room for the mercy seat; and the plan of all that he had in mind for the courts of the house of the Lord, all the surrounding chambers, the treasuries of the house of God, and the treasuries for dedicated gifts." (I Chron 28:11-12)
After the ascension of Jesus, the disciples return to Jerusalem and go to the upper room in which they staying, devoting themselves to praise and supplication. In the Book of Acts, the upper room is where Peter performs miracles. In the Book of Mark, the disciples are instructed to follow a man, who has prepared an upper room for them for Passover. This Upper Room (The Cenacle) is understood by Catholics to be the first Christian church: certain resurrection appearances of Jesus are placed here; this is where the preparation happened for his final Passover meal; this where Jesus washed the disciples feet; this where the Holy Spirit fell upon the disciples on the day of the Pentecost.