Ingrid Wassberg, 65, discovered the snake as she was going onto her balcony Monday in Karlstad, Sweden, The Local reported.
"I looked down and saw something I didn't recognize, and I realized it was a snake," Wassberg said.
She quickly ran back inside her apartment and managed to snap a few pictures for the police, whom she called within minutes of catching sight of the boa.
Police had to call an animal expert to remove the snake from the apartment building. The handler transported the serpent to a local pet store, where it was being held until its owner is identified.
Wassberg says she has not heard of anything like this happening to her friends or neighbors.
"I don't really like snakes, so it was a relief when it was taken away, but I checked for more snakes here just in case," she said. "I've gone around and looked and have not seen any, so it's a bit of a mystery."