These four walls
Definition 1 of 2
Pro Tip 1/3Loneliness Emphasis
Expresses a feeling of solitude or isolation within a confined area. 
After weeks without guests, these four walls seemed to echo her loneliness.
Pro Tip 2/3Seeking Connection
Used when someone is craving social interaction or company. 
Calling her friend, she said she couldn't stand these four walls anymore.
Pro Tip 3/3Mood of Space
The phrase often relates to the mood one associates with a room. 
His studio, once vibrant, felt lifeless – just these four walls and silence.