Every year, casual onlookers become architecture buffs at this free event (October 19 and 20), in which the Chicago Architecture Center offers access to otherwise restricted buildings. Here is our doable-in-one-afternoon recommended itinerary, featuring two new sites. All are open Saturday and Sunday, 10 a.m. to 5 p.m., unless noted. For the full list, visit openhousechicago.org.

1 The Second City

For the first time in OHC history, you can trace the steps of comedic legends. The self-guided tour leads you through the three main theaters and points out hidden memorabilia gems. Get in character and plane, train, or automobile to your next destination.
Details:1616 N. Wells St.

2 Essex on the Park

Overlooking Grant Park is one of the South Loop’s newest residents — a 56-story luxury tower, open since March. The tour includes a four-story glassed-in garden, in which you are free to nap — er, walk around.
Details:808 S. Michigan Ave.

3 The Conservation Center

Hidden in a nondescript warehouse is the country’s largest private art conservation lab. At this Studio Gang–designed workspace, you can watch the work of those who brought back to life Salvador Dalí prints, suits of armor, and Abe Lincoln’s couch.
Details:400 N. Wolcott Ave. Closed Sunday.

4 Héctor Duarte Studio

This Mexican American artist is behind more than 50 vibrant murals around town, concentrated in Pilsen. Duarte invites visitors to his studio to see in-progress work inside and to learn just who is painted on the outside.
Details:1900 W. Cullerton St. Saturday: 10 a.m. to 4 p.m.; Sunday: noon to 4 p.m.

5 The Forum

Once a linchpin of the Black Metropolis, this long-vacant ballroom is finally being restored after four decades. A rep from Urban Juncture, the developer, will discuss the history and future of the venue, which hosted everyone from Nat King Cole to the Freedom Riders.
Details:324 E. 43rd St.