The upstairs parlour was the room which was sealed off in real-time, but led to the parallel time band.
One can assume the room existed when Collinwood was built in 1795, but in the real-time continuum, it was sealed off by 1840. In 1840 and 1970 a few people passed through the room and into parallel time, but only briefly, except for Barnabas Collins who spent a few months there, and Lamar Trask, who died there.
In 1841PT, the house had been built in the 1600s, and it is not known when travelling to alternate universes began. If 1841PT and 1970PT were in the same time band (doubtful), then there may have been other travellers, but they are not known.
In 1841PT, the room was used for relaxing with family, as opposed to the Drawing room where business and serious events were conducted and where people outside the household were met. It was here that Justin Collins attacked Stella Young (1204). It was here that Gabriel Collins planned to escape, and a mortally wounded Lamar Trask.
In 1970PT, this was known as Angelique's room. If one knew where to stand in a nearby room, they could make the Portrait of Angelique Stokes Collins appear to speak. It was preserved after Angelique's death by her fiercely loyal servant, Hoffman. It was in this room that Elizabeth Collins Stoddard (PT) was murdered by her brother, Roger Collins (PT).