This event on Pentecost begins in a house where the disciples were “all together” (v. 1).8 It is not made clear whether this is the same location as the “upper room” where the Last Supper was eaten, or where the disciples were staying (cf. 1:13). There is some interesting evidence of the validity of the tradition that the place on Mount Zion is now known as the Cenacle was the location where the earliest Christians met and that it quickly became a holy site, a place for ongoing Christian worship. Somewhere along the line, the event migrates to the temple precincts, the only place such a crowd could or would likely be congregated, but Luke does not explain the sequence, only the events.
Witherington, Ben, III. The Acts of the Apostles: A Socio-Rhetorical Commentary. Grand Rapids, MI: Wm. B. Eerdmans Publishing Co., 1998. Print.