What now are comfortable patios outside bars and restaurants in Lower Downtown, once were part of an underground network of tunnels that allowed affluent folk to travel by horse and buggy from Denver Union Station to hotels and businesses in the blocks nearby. They’re an incognito part of Colorado’s heritage that is at risk of being lost.

Denver’s downtown underground — along with subterranean places in other cities across the state including Grand Junction, Durango, Fort Collins, Pueblo, Salida, Florence, Cañon City and Trinidad — made Colorado Preservation Inc.’s 2018 Most Endangered Places list.

Back in the 1880s, before the car was invented, the tunnels were used by the wealthy, allowing them to avoid grime and thievery when they arrived in Denver. As soon as the automobile was invented, however, the tunnels took a turn for the worse. While the well-heeled folks were safe in their cars, thieves and prostitutes took to the tunnels where they committed robberies and homicides.

“They had tunnels that would lead from Union Station and they had tunnels that would go all around town,” said author Tracy Beach, who for five years researched Colorado’s hollow sidewalks and vaults for her book, “The Tunnels Under Our Feet.” “Buildings were built in the mid- to late-1800s and the tunnels were built as an extension of their basements.”

While most of the tunnels have been sealed off or filled in — purposely or through silt from flooding — some businesses still have access to the entrances of musty caverns that used to go on for miles.

You can see them from 17th Street in front of the Oxford Hotel, or get a hint from steps built of glass bricks in front of Blake Street Vault at 1526 Blake St. In Cripple Creek, the tunnel openings are evident from the ruins of the foundation of the lost opera house.

Many businesses leave their basements unfinished, preserving the entrances — like at the Oxford, where a maze of uneven stairs descends to a remodeled room where a tiny door opens to a narrow, dark hallway longer than the light from a flashlight could reach.

But some buildings have filled in the hollow areas under their sidewalks to add more square footage, perhaps unaware that it’s a part of history.

“There’s so many little towns that have these below ground areas and they’re just being destroyed. The more people that know they exist, the more, hopefully, we can stop destroying them,” Beach said. “We need to appreciate them and open them back up.”

Other cities across the nation are using their history to their advantage — instead of making the areas in front of businesses into a sitting space, they’re are making them into a learning space.

“People pay a bunch of money to go in these tunnels,” Beach said. “People go and spend like $20-something a ticket just to look at underground Seattle. Accept the fact that these things are historic, they’re really cool, and they’ll bring tourism.”

Every year Colorado Preservation, Inc. highlights a number of historic locations that are in danger of being destroyed. CPI announced their locations at the Saving Places Conference, a four-day event that features high-quality educational sessions and workshops, tours, and networking opportunities.

The other places on the 2018 list are:

Doyle School (Pueblo County)

The Doyle Settlement was established by Joseph Bainbridge Lafayette Doyle in 1859 when he purchased 1,200 acres of land along two miles of the Huerfano River from the Vigil and St. Vrain Land Grant.

The Doyle Settlement retains the cemetery and school building and is a beacon overlooking the Huerfano River Valley at the very southern edge of Pueblo County, about 25 miles southeast of Pueblo. The cemetery is one of the oldest burial grounds in Colorado and contains the gravestones of the Doyle family, early pioneers and other members of the Doyle Settlement. The schoolhouse is one of the oldest in Colorado.

Historic Elk Creek Octagon & Barn at Shaffer’s Crossing (Jefferson County)

This region is named Shaffer’s Crossing because it marked the area on the Shaffer’s property where the old stagecoach route crossed Elk Creek.

The architecture of the Elk Creek Octagon Building — with only six sides — is unique for its steeply pitched roof, reminiscent of older European churches, supported by a 35-40 foot tall pole at the middle. The remnants of hand-painted flowers and wildlife remain on ceiling panels.

The family home, store, and Episcopal-Methodist Church are long gone, making the Octagon Building and barn with purported ties to the outlaw Butch Cassidy, the remaining familiar landmarks on the site, highlighting the case for their preservation.

Tarryall-Cline Ranch (Park County)

The ranch house is a Park County landmark located between the towns of Como and Jefferson. The main ranch house was built in 1928 by Foster Cline Sr., a prominent Denver attorney.

Architecturally the main ranch house is an example of the Pueblo Revival style with elements of the Spanish Eclectic Style which is very unusual and rare for a ranch house in Colorado from the first half of the 20th century.

The initial goals for the ranch house include stabilization and protection from the elements and potential vandalism.