Doors Open Minneapolis offers the keys to buildings — or spaces within buildings — that are often closed to the public. Think behind the scenes, backstage, below ground.

Sure, you can buy a ticket to a concert at the Cedar Cultural Center. But during Doors Open, you can also check out the venue's green room, where the artists hang.

Last year's free event, the first since 2019, brought 14,000 people to 87 locations across the city. This year's event is even bigger, with 105 venues.

It's run by Rethos, formerly the Preservation Alliance of Minnesota. That organization "used to focus a lot on buildings," said Kelly Fischer, heritage tourism manager. "And of course, it still does. But ultimately, the field of historic preservation has started to gear more towards the stories of people that inhabit those buildings.

"Because the buildings have a lot less meaning when they're not attached to story and culture and history."

Half of the event's venues are historic. There are plenty of old churches, theaters and homes. But many of those historic spaces are hubs of activity. The Star Tribune's printing press was "a huge hit last year," Fischer said. Last year, it was open only on Saturday and "got absolutely slammed." So this year, it will be open both days.

Some tours require tickets, but all venues are free. Buses and light-rail are free, too, and there are 10 free parking ramps and lots, mostly downtown. The event runs Saturday and Sunday, but not all venues are open both days. More information can be found at www.doorsopenminneapolis.org.

Here are three ways to explore:

If you love planes, trains and automobiles:

Check out the Minneapolis Traffic Management Center, where experts use up-to-the-minute traffic surveillance and other tools to manage how cars move throughout the city. Stop by the Metro Transit Blue Line Operations and Maintenance Facility on Franklin Avenue, where tour guides will "teach you how the system runs and how we keep it in tip-top shape." Then go to the Lift Garage on E. Lake Street, an auto repair shop that offers low-income people low-cost car repair. There, technicians will explain tools and parts, putting cars on lifts to show kids and adults alike what they look like underneath.

If you want to explore Black history:

Start in North Minneapolis at the Capri Theater, one of this year's new venues, to see the stage where Prince performed his first solo show. Stop by the Minnesota Spokesman-Recorder to "experience the rich history of this black press," via tours, photos and old papers. Then make your way to south Minneapolis to the historic Coliseum Building on E. Lake Street, another new venue. The 1917 building has long been a hub for Black businesses. Burned during the riots after the police murder of George Floyd, it just got a $28 million reconstruction. This tour offers a first look.

If you want to peek underground:

Sure, this event gives several chances to see the city from a tall perch. (The Foshay Tower's 30th-floor observation deck is a favorite.) But the event also offers a look below. The city of Minneapolis will be sending a camera down a sewer manhole on Nicollet Mall and setting up a closed-circuit television truck so that passersby can see the inside of the sewer system. Then, travel 82 feet beneath the Elmer L. Andersen Library to explore the Minnesota Library Access Center, a subterranean library of 1.5 million volumes. It's one cool cave.