Milwaukee – presumably like most cities – is full of stories of hidden places.

It seems nearly everyone has a story of a tunnel connecting this to that, or of caves beneath their neighborhood. And darn near everyone living in a 100-year-old home believes their place was once a boarding house or speakeasy. So, you’ll understand why I view each of these stories with a mix of intrigue and skepticism.

Decades ago, driving on Greenfield Avenue with my grandfather, we reached that rise that begins to climb around 30th Street. Pointing to the building perched atop the crest of the hill, my grandfather told me there was a tunnel running to it.

Thanks to Doors Open’s Amy Grau – who brought me and architect Keith Stachowiak along for the adventure – I walked through nearly the entire length of that tunnel, proving my grandfather’s story correct.

The tunnels connect the St. Joseph’s Convent complex at 1515 S. Layton Blvd. to the building up on the hill a few blocks to the west.

The St. Joseph and Perpetual Adoration Chapels will be open again during Doors Open 2014 – they were open both previous years, too – but the tunnels are off-limits to the public.

Before we go down there, let’s talk history.

The School Sisters of St. Francis arrived at the site in 1886 from Germany, by way of Campbellsport and Winona, Minn., buying the private Greenfield Park beer garden from Joseph Knurr with an eye toward building the order’s motherhouse on the site.

The first structure, built in 1887 had space for 300 nuns, but burned barely three years later. The order then hired Herman P. Schnetzky to design a replacement that was apparently similar to the previous convent.

That building is still there – be sure to go around the back, to 29th Street, to see Schnetzky’s fine rotunda – and has been added to numerous times. The most obvious and magnificent addition is the Romanesque Revival chapel designed by Brust and Philipp and erected from 1914 to 1917.

Technically, the building, with its squat octagonal dome, is a chapel, because it has no entrance from the street, but the word "chapel" conjures something considerably more modest.

It is said that the architects toured Italy as research for this commission.

Top-loaded with relics preserved in reliquaries in the sanctuary, in the adjoining Chapel of Perpetual Adoration and in a connecting relic chapel, the main chapel even has the entire earthly remains of 3rd century martyr Saint Leoninus preserved in the Sacred Heart altar to the left of the main altar. Nearby is a fragment of the true cross.

The ceiling above the altar is painting in stunning blues and gold and impressive mosaics adorn the altars of the main chapel and the smaller Perpetual Adoration chapel.

Russell Zimmermann calls St. Joseph’s Chapel "the finest of Milwaukee’s Romanesque Revival churches," and I’m hard pressed to dispute that.

Also part of the complex – which serves as the international "headquarters" of the School Sisters of St. Francis – is the former Sacred Heart Sanitarium, dating to 1893 when the nuns opened the building as a health spa that was open to the public. Alas, the original building was razed in 1977 and replaced with the current structure.

Also behind the convent and chapel is the unusual two-story cream city brick building that is home to Ebenezer Day Care Center. When we arrived, Keith and I were both struck by its unusual jerkin-head gable roof and wide doors that suggested it may have been a coach house at one time. On the north facade, discoloration on the bricks outlines what appears to have been a wooden porch.

The 1910 Sanborn map calls the structure "summer sleeping rooms," though it also housed stables. Rumor has it that the building was a Greenfield Park dancehall.

Our tour guide, Michael O’Loughlin, knows we’re champing at the bit to see the tunnels and he leads us through a heavy, unmarked wooden door and down two flights of steps.

We’re in the basement of the convent building, where there are storage lockers and wide hallways with low ceilings. We walk perhaps 200 feet and pass through a door and up a half-dozen steps. I can see through a window that we’ve headed a bit southwest, past the corner of the chapel and we’re on our way through a tunnel to the basement of the sanitarium building.

Heating pipes hiss, and we can hear running water in other pipes and we follow the red line painted down the middle of the floor that shows the path between the Sacred Heart Center and the St. Joseph Center.

We enter another tunnel, having exited the Sacred Heart Center basement and we’re on our way west. The tunnel is now narrower, with an even lower ceiling. At 6-feet-tall, I don’t have to duck, but I’ve got to mind the ceiling. If I reach my arms straight out to the sides, I’d easily touch both walls.

It’s a little damp, but not much, and it’s still warm because heat pipes run along the wall. There are lights.

The tunnel is mostly straight, but it does bend a bit here and there. We continue walking and the ceiling takes on an arched shape.

It's interesting that the tunnel doesn't appear to follow Orchard Street, but rather runs beneath rows of private homes that line the street.

Nothing much changes in the tunnel, but I’m eager to keep going. It’s a tunnel, right? It leads somewhere, so let’s go see.

Finally, perhaps a quarter mile from where we started, there are stairs up to a doorway on the right and light seeps in around the doorframe. Our guide tells us this is a house on South 32nd Street where some of the sisters live.

Straight ahead, the tunnel continues but there are no more lights, so we decide to turn back. We can’t tell how much longer the tunnel runs. I head out into the sunlight and see that the building where the tunnel terminates is directly across 32nd Street from the nuns’ residence.

"The building was built in 1912 as a psychiatric hospital and was intended to complement Sacred Heart Sanitarium to serve the laity who had mental afflictions," says O'Loughlin. "It was called St. Mary’s Hill Hospital."

"In the 1980s those services were transferred to St. Mary’s Hospital and School Sisters of St. Francis began to use it for retired and infirm sisters. We then called it Maryhill Health Center. In 1995, when Sacred Heart Hospital was also transferred to St. Mary’s Hospital, we moved all the Sisters to Sacred Heart. In 1996 we sold the building to Seeds of Health."

Seeds of Change runs a high school and a WIC program on the site.

So, that dark tunnel didn’t run much further, and we wouldn't have been able to exit it into the old Maryhill Health Center.

Still, I’d have been willing to check it out.