DOWNTOWN — One weekend a year, the owners of Chicago’s coolest buildings throw open their doors and invite people inside.

It’s a chance for people to scratch that itch: I wonder what THAT place looks like on the inside.

And take tons of photos.

This year’s Open House Chicago is being held Oct. 13 and 14. It’s sponsored by the Chicago Architecture Center and is wildly popular … and free.

SEE THE ENTIRE LIST OF OPEN HOUSE CHICAGO LOCATIONS.

You don’t even need to register for most of the sites. Just show up during the scheduled hours. (There are a handful of “members only” locations and RSVP spots. Click here for the entire list.)

There are events in neighborhoods all over the city, with more than 250 buildings in 30 neighborhoods on the schedule.

Highlights? Who’s to say. So many of the buildings are architectural gems with tons of history to learn. But we’ll list a few that caught our eye.

The Blackstone Hotel, 636 S. Michigan. Ave., South Loop. You’ve probably passed by it tons of times, but you should really see the ornate lobby.

House of Blues Foundation Room VIP Club﻿, 330 N. State St., River North. This catacomb of tiny upstairs rooms is fascinating.

McCormick Bridgehouse & Chicago River Museum, 99 E. Riverwalk (Michigan and Wacker). The Riverwalk. There’s a museum inside that old bridgehouse?

Assumption Greek Orthodox Church, 601 S. Central Ave., Austin. Built in 1937, it’s the building with the distinctive green dome.

The Givins Castle, Beverly Unitarian Church﻿, 10255 S. Seeley Ave., Beverly. The “Irish Castle.”

Ling Shen Ching Tze Buddhist Temple, 1035 W. 31st St., Bridgeport. Designed by John Wellborn Root and completed by Daniel Burnham, it’s been home to this Buddhist school since 1992.

The Forum, 324 E. 43rd St., Bronzeville. Nat King Cole played there, and it’s in the process of being restored.

Edgewater Beach Apartments, 5555 N. Sheridan Road, Edgewater. Not to be confused with the long-gone Edgewater Beach Hotel, this pink building was its next door neighbor.

St. Benedict the African Roman Catholic Church, 340 W. 66th St., Englewood. Has one of the largest baptismal pools in the country, with 10,000 gallons of water.

Great Lakes Yard, 2651 W. Lake St., Garfield Park. Located under the Green Line tracks, it houses salvaged wood waiting for a new life.

KAM Isaiah Israel, 5039 S. Greenwood Ave., Kenwood. This soaring domed temple has very famous neighbors: The Obamas.

Airstream Building, 1807 W. Sunnyside Ave. Lincoln Square. It’s the office building with the Airstream on the roof.

Nichols Tower at Homan Square, 906 S. Homan Ave., North Lawndale. The old Sears Tower still stands proudly, and has an incredible top floor ballroom.

WHAT’S HAPPENING IN YOUR NEIGHBORHOOD?

♦ Bridgeport, Chinatown

♦ Downtown

♦ Lakeview

♦ Lincoln Square, Ravenswood

♦ Pilsen, Little Village

♦ Rogers Park and Edgewater

♦ West Loop

♦ Wicker Park, Bucktown, West Town

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