Why do guests avoid the seventh room?
In Edgar Allan Poe's short story "The Masque of the Red Death," Prince Prospero has gathered his friends and sequestered them within an abbey in order to protect them from the epidemic of the "Red Death." After five or six months of isolation, Prospero decides to throw a masked ball to entertain his guests, complete with an imperial suite of seven rooms.
The seventh room is described as being covered in black velvet tapestries and carpeting; it contains a giant ebony clock which emits loud music as each hour passes. Only the windows stand apart from this dark color, with their panes taking on a "deep blood color." The lighting which comes from the hallway illuminates the room to "ghastly" effect and produces a wild facial expression on those who enter it. Thus, guests avoid the seventh room simply because it is terrifying--a stark reminder of the plague which has wiped out the population outside the abbey's walls.
"The Masque of the Red Death" has a surreal tone, and as such, cannot be read in a strictly literal sense. The obvious answer is of course that guests avoid the seventh room because it is scary. The other six rooms each have their own color and theme; they are welcoming, fun, and what one would expect of a party. The seventh room, however, is covered in black velvet, and unlike the other rooms where the windows match the walls in terms of color, this is the only room with a dual-tone theme. The black walls are illuminated by blood red windows. This is also the location of an ebony clock, which is not frightening in itself, but with each passing hour, this particular clock causes a wave of fear to spread through the party. This setting is enough to scare anyone off, especially when there are so many more cheerful rooms to spend time in.
However, the aversion to the seventh room is deeper than mere appearances. Think about the reason these guests are here. They are hiding from the outside world in order to avoid contracting the "red death," the plague sweeping through the country. A death-colored room with red windows will no doubt cause a type of association that would subconsciously cause partygoers to avoid the room. After all, who wants to stay where the very light is the same color red associated with the disease they are so afraid of?
Deeper meaning can be read into the story in terms of class differences. These partygoers are the rich, the upper class, the ones who have the money to survive by hiding. It is the poor who die from the plague; it is the poor who succumb. The story alludes many times to the extravagance of the party and the tastes of the prince who throws it, yet there is next to no dialogue or description about what happens on the other side of the castle walls. These people clearly do not concern themselves with the possibility of the plague reaching them. They worry about the party; they worry about the seventh room, for it does not quite fit with their usual merrymaking.
This fear of the seventh room is as close as these people get to thinking about the real "red death". It is the thing that breaks their dreamlike living situation behind the castle walls, the thing that brings back reality. It is no accident that the prince dies in this room from the plague. When the masked guest is revealed as the plague itself within this room, it is merely giving voice to the unnamed fears associated with the seventh room. It is the site of the broken protection of this wealthy group and what ultimately causes them to awaken.