The Stairs To The Basement?
 

Hello.
The TARGET which is on the living area's floor could be the access to the BASEMENT.
The target could open, leading to the spiral staircase as the target is spiraled.
ALSO when Davina stood on the target last night she said something on lines of..."DON'T STAND ON THE TARGET HMMM" in the way as if something would happen.
What do you think?

You can see by the picture its set firmly into the floor and is made of the same rubber material as the rest of the floor.

The housemates would have discovered some crack or gap in the material or texture by now.

It doesn't look like it is any access, it looks set to the ground.

The stairs to the basement could be behind the door in the black and white entrence room

Thats what i thought

i thought the enterance was the door next to the kitchen you could see in that picture..

but maybe its the door to the kitchen.