You can usually only get past security into the Upper St. Anthony Falls Lock as part of a tour.
But for "Illuminate the Lock" events, the gates will be thrown open when the massive dam is used as a giant projection screen.
"I think it will work a little bit more like a gallery experience," but one in which people can walk the perimeter around the top of the lock, said Katie Nyberg executive director of the Mississippi Park Connection, which is co-sponsoring the show.
It's hard to gauge just how big it is until you stand on the edge, said artist Aaron Dysart. It's 500 feet long, 50 feet tall, and almost 45 feet across. A friend of Dysart's put it in perspective for him.
"He came out and he's like 'Aaron, what you are looking at here is a 50-story building on its side. On its side. It's 500 feet long," Dysart recalled. "And that's when it really hit."
Dysart works with light and data. His piece, called "Surface," will show this Friday and Saturday nights. He wanted to celebrate the structure, which has been in place since the 1960s a navigational aid and flood-control tool.
"What I envisioned was to work with the logbooks that the Army Corps of Engineers kept," Dysart said.
So, he filed a Freedom of Information request for the logs with the Corps, hoping for spreadsheets.
"What I got was roughly 47 to 50 textbook-sized books where each page represented a day in the life of the lock," he said.
The books represent roughly 10,000 pages, recording what the lock keepers did on a daily basis. Dysart ended up focusing on the six daily readings the keepers took of the water level in the pool below the lock.
He built that information into a program controlling four main floodlights that brighten and dim depending on the pool height on a particular day. The light is purple and will play on swirls of strategically produced mist. "The math works out that every day in the life of lock will be half a second in the light show," he said. "Then when the calendar year turns around, there will be fog machines, suspended on either side, and they will give a 30 second burst of fog, filling the chamber with atmosphere that those lights will catch on."
Dysart hopes the experience will not only get visitors to think about the history, but also the future of a public structure. The lock was closed to navigation in 2015, although it can still be used for flood control.
Andrea Carlson, the second "Illuminate the Lock" artist, is more interested about what came before the lock.
"I don't really feel bad about the Upper St. Anthony Lock and Dam because in order for the ships to go through, they took out Spirit Island," she said.
Spirit Island was a site sacred to Dakota people. It was a limestone island just downriver from where the Stone Arch Bridge now stands. It was gradually removed over many decades, despite objections from the Dakota people and Minneapolis residents who picnicked there.
Carlson, who is Ojbiwe, named her project "The Uncompromising Hand." It's a quote from a Minneapolis paper article published in 1900 that complained about how the uncompromising hand of industrialization sacrificed a beloved spot.
"My project is projecting images and drawings into the shaftway of the lock and it's kind of to remember that," she said.
National Park Ranger Dan Dressler, another co-organizer, hopes the events will help people who come to the Stone Arch Bridge and St Anthony Falls see the lock differently.
"We are going to light it up, and it's going to become an icon, right next to all these other icons along the river in Minneapolis," he said.
If you go
• Dysart's project runs Friday and Saturday.
• Carlson's project runs on Sept. 29 and 30.
• All four performances are free, and run from 8:30 p.m. to 10 p.m.
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