These pillars of Chicago infrastructure have been off-limits to the public, doubly so since 9-11, which only amplifies on the mystery of these brick cabins sitting amid Lake Michigan. Built in the 19th and early 20th centuries as water intakes, and positioned far enough away to avoid pollution near the shore, these man-made concrete-and-brick islands used to be manned by small crews of utility works until the early '90s (the kitchens and bunkrooms weren't half bad). Past Tribune articles spoke of crew members working to keep fish out of the intake valves, and occasionally using small dynamite charges to break up frozen ice.

Now, does this sound like your CTA: spend millions building a massive underground station in the Loop, meant for express trains that service both of Chicago's airports, only to discover the plan would require massive overhauls of existing rail lines and stations, making it economically unfeasible? That's basically the story of how Chicago ended up with the Superstation, a huge, empty concrete shell. Chicago Magazine writer Greg Hinz, one of the few people to tour it, called it “one of the world’s biggest unfinished basements.” Secret subterranean lair or a monument to bad city planning, it still would be an incredible place to tour, if only to imagine what could be done with such a huge space.

Founded in 1905 by Ukrainian immigrant Isidore Horween, Chicago's last operating tannery produces an array of leather goods, from pro footballs to watch straps for Shinola. Numerous institutions can boast of a connection to the city's industrial past, but at this brick building near the north branch of the Chicago river, the dirty factory floors and metal hoppers are still humming with commerce and industry.

Housed in an old car dealership built in 1925, when showrooms for cars were designed like movie palaces, Richard's Body Shop offers a level of ornamentation rarely seen in retail. Originally the home of Capitol Motor Sales Company, Isadore and Isaac Burnstine constructed this auto palace in the '20s with elaborate ornamentation, from the magnificent terra cotta façade to a Mediterranean-inspired interior overrun with inspired flourishes. You'll want to skip the Carfax and instead learn more about the over-the-top design.

Finding accommodations fit for the Pope can be challenging. Luckily, when Pope John Paul II stopped by Chicago in 1979, he could turn to the Archbishop's Residence in the Gold Coast, a massive brick mansion built in 1885. Boasting 19 chimneys, 35 rooms, a coach house and a private chapel, it offers quite the lush life for a humble servant of the Lord. It stands as one of the oldest mansions in the Astor Street historic district.

According to a Tribune series about unauthorized places, a small control room at the southeast edge of this iconic landmark houses the Honeywell Excel-Plus computer that controls the flow of the famous fountain. Below that sits a massive bunker of a room that contains the three pumps that power the fountain. All the motors and pumps are still the originals that were installed in 1927; replacing them now would require a custom machined replacement.