Just days after moving into a spacious, three-level, apartment in a swanky Murray Hill building, a woman turned the triplex into a flophouse for rent, with bunks lining the walls and Internet ads to attract tourists, a lawsuit charges.

An adjoining tenant discovered Tae Kyung Ha’s allegedly illegal hotel after one of her guests asked to use his private terrace and he peeked through her window, the owners of the East 36th Street building claim in court papers.

The apartment “resembled a military barracks, rather than a luxury residential apartment,” the suit by 36 and 37 Realty says.

“We didn’t know it was against the law” to rent out beds in the apartment, Ha’s son, Sky Kyung, 22, told The Post, adding that she paid a year’s rent upfront.