A hotel guest who complained after catching a manager watching her undress through the window was offered a free night's stay as compensation.
Saleswoman Clare Day, 27, was naked in the ground floor room when she spotted the peeping Tom's face "pressed against the glass".
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She said: "My stomach lurched. It was like something out of a horror movie.
"I was in the bathroom and saw him behind me through the reflection in the mirror. I screamed and covered myself. I knew it was the man who'd checked me in. Then his face disappeared."
When the married mum of two phoned the Best Western reception she was told to lock her door and report the incident in the morning.
"I was so scared I pushed a wardrobe against it to block it, but I still didn't sleep all night," said Clare.
It is believed the shift manager, who had tried to chat to Clare that night as she ate in the restaurant alone, was sacked after CCTV footage was found.
It was handed to police and Clare pressed charges, but the man was only given a caution for voyeurism because it was a first-time offence.
Clare, of Kirkby, Nottingham, said: "I'm furious. He has been let off scot-free. I felt totally violated and I am still suffering the effects of his actions."
She said the ordeal left her so shaken her husband Nick, 31, took two weeks off work because she was afraid to be alone.
A Walworth Castle spokesman said: "It is not our policy to comment on individuals or individual matters in relation to Walworth Castle."
A Durham Police spokesman confirmed: "A man in his thirties was questioned by police on suspicion of voyeurism and accepted a caution."