Seattle police are searching for two men who climbed over the glass wall of the Space Needle on July 24 and parachuted from the 605-foot structure.
The Seattle Police Department said the jump was reported at about 9:21 p.m., and officers who arrived contacted two Space Needle security guards; the men had purchased tickets and entered at about 8:50 p.m.
Police said surveillance showed the men on the top level, then entering a restroom and emerging with helmets before running to a glass window facing northbound, with Lake Union in the background, climbing over to the other side and doing a back flip off the ledge.
"We are aware of an illegal incident at the Space Needle and are working closely with the Seattle Police Department," the landmark said in a statement. "We are reviewing security footage and assisting with the active investigation."
The jumpers face trespassing charges, a report provided by Public Affairs Officer Brian Pritchard said, and authorities have not identified them; they were described only as white men in their late 20s.
Space Needle security were unsure where the men landed, and police could not locate the individuals after the jump, officials said.
Videos captured by visitors and shared on social media show two people reportedly BASE jumping from the observation deck.
BASE jumping is an extreme sport that involves leaping from fixed objects and deploying a parachute; the Space Needle observation deck is located at 520 feet above the ground.
It was not immediately known whether either person who jumped was injured, and anyone with information about the incident is asked to call Seattle police at 206-625-5011.
The stunt came just over a month after two people died in a BASE jumping incident in Utah on June 14, the Grand County Sheriff's Office announced; the agency identified the first victim as Andy Lewis, 39, an extreme sports athlete.