Tens of thousands of people drive by the Colorado State Capitol every day, but have you ever been inside?
We went behind locked doors to learn the secrets of the Capitol including what’s in the underground tunnels, why there are two domes (yes, there are two!) and how crews are able to add a skylight to the House and Senate chambers.
Secret No. 1: There are two domes on the State Capitol. There’s the gilded dome you see from the outside and the rotunda dome you see from the inside.
From the public observation deck, workers go up three sets of stairs to what’s called the attic.
In the attic, you can see the top of the rotunda dome and you are surrounded by the golden dome.
Secret No. 2: The top of the rotunda dome actually rises.
When the Capitol was built, heat came from the basement, up through the north and south wings. Air then flowed into the dome. This top section of the dome was hoisted up a few feet to allow heat to keep rising up and go out the windows in the top of the capitol – the area called the lantern.
Secret No. 3: The names on the walls of the “attic” room are the people who re-gilded the dome over the years. 
There are names from the 50s, 80s, 90s and 2013.
There was graffiti on the walls that was removed during the last renovation, but a few spots remain including this inscription from 1896 on a beam.
From here, there are more stairs to the lantern and those windows that opened for ventilation.
From here, you can look down on the golden dome.
And there's more thing in this room... hooks.
The hooks were installed for the gilders to use when they hung on rope on the side of the Capitol to add the gold on the dome.
Secret No. 4: The dome is not gold – it’s copper covered in gold leaf.
The copper dome was originally installed in 1894, but by 1908 it had turned black.
“It was not aging gracefully,” said Department of Personnel and Administration communications manager Doug Platt.
Officials decided to replace the copper plates and gild the plates in gold. Over the years, the gilding was replaced and in 2013 the copper was replaced for the first time since 1908 and regilded again.
Secret No. 5: The top of the Capitol was supposed to be a 12-foot high statue of a woman. 
However, legislators couldn’t agree on the design, so the top of the Capitol is a crystal sphere also known as the lantern.
It turns out, during renovations, two of the 16 panels needed to be replaced, but modern-day crystal manufacturers couldn’t replicate the curved panels. 
So now the crystal lantern has 14 crystal panels and 2 glass panels.
From the top of the dome, let's head to the bottom of the building.. underground.
Secret No. 6: There are tunnels under the capitol and yes, they are still in use.
The Capitol was coal heated in the late 1800s and early 1900s. Wagons used 14th Street to bring coal in and take the coal ash out. However, some thought that was unsightly, so tunnels were dug underground to move the coal ore carts.
If you look closely, you can still see the ore cart tracks in the concrete of at least one tunnel.
Today the tunnels are used for utilities – steam heat, power and phones. Platt says there’s no truth to the rumors that the tunnels were used for nefarious reasons. Platt says the tunnels lead to several of the Capitol complex buildings.
Secret No. 7: There are vaults in the sub-basement of the Capitol. 
The vaults were installed in the granite walls of the State Capitol because the building once held the state Treasury. When the treasury moved out, most of the vaults were left in place. Now, the rooms are used for storage.
Secret No. 8: The Colorado State Capitol has a geothermal power plant in its sub-basement.
Platt said this is the first state Capitol to use a geothermal system to both heat and cool the building. The water comes from an aquifer below the Capitol and after being used, the water is returned to the aquifer so there is no loss of water.
Secret No. 9: As we walked into the geothermal room, we spotted dozens of air conditioners stacked up in the hallway. 
Platt said the window units are installed in Capitol offices in the late spring/early summer to help keep the offices cooled. The air conditioners are removed in the fall.
Let’s move up to the main floors and head into the House chamber where big changes are underway.
Secret No. 10: A crooked radiator led to a major overhaul of the House and Senate chambers.
Back in 2012, then-House speaker Frank McNulty asked chief clerk Marilyn Eddins about a crooked radiator in the gallery of the House chambers. Eddins said McNulty wanted the radiator fixed and told her to check on the tiles around the chamber, too. That led to a joint a project with the Senate leaders.
In 2014, the tiles on the walls in both chambers were replaced.
Secret No. 11: An expert looking at the paint on the walls noticed there was another texture below the surface. Experts from the Denver Art Museum brought in an infrared camera and found shields and other images in the layers of paint.
This year, the ceilings are being redone in both chambers and skylights are being added.
Secret No. 12: There’s a skylight above the House chamber and the Senate chamber, but you can't see them from inside the chamber. Both were covered in the 1950s.
You can see the skylights in the attic.
Over the next few months, the ceiling tiles are being replaced and the skylights will be restored so they can be seen from the chambers and bring in extra light.
Secret No. 13: The chandelier in the House chamber is gone. 
It was removed, piece-by-piece, on Monday and is being sent to St. Louis to be restored.
Before the chandelier was removed, restoration expert Gary Behm, founder of the St. Louis Lighting Company, said the chandelier originally had gas lights, but was rewired in 1956.
“The gas arms went up and they added electric below,” Behm explained. “It’s gone through some rough times and we’re here to restore it.”
Because Behm can only do one project at a time, the chandelier in the Senate chamber won’t be restored until next year.
Let’s head up to the public observation deck.
Secret No. 14: The public tours no longer take the 99-rickety steps to the observation deck that they used for years. 
During the recent remodeling, new staircases were added to Mr. Brown’s Attic (a history museum) and the observation deck.
At the top of the stairs, notice the exits to the deck aren’t doors that swing open – they’re windows that lift up.
Out on the deck, look at the columns and the walls outside.
Secret No. 15: Those columns aren’t stone, they’re cast iron that’s been painted over. Look even closer at the columns and walls and you’ll still see places where the cast iron isn’t perfectly smooth or where there were rivets. 
Platt said they left the imperfections because it’s part of the history of the building.
Hear more stories and see more of the Capitol on a free tour from 10 a.m. to 3 p.m. Monday through Friday. Learn more here.
Check out more of our secrets of Colorado stories:
- 17 secrets of the Eisenhower Tunnel and Johnson Tunnel
- 9 secrets of Denver's Union Station & the Crawford Hotel
- 15 secrets of the new Denver International Airport Westin Hotel project
- 17 secrets of Coors Field
- 10 secrets of the 16th Street Mall Clocktower
- 12 secrets of the Furniture Row NASCAR garage in Denver
- 7 secrets of the Wild Animal Sanctuary
- 7 secrets of Rockmount Ranch Wear
- 11 secrets of the History Colorado Center
- 10 secrets of the Federal Reserve Bank in Denver
- 7 secrets of the National Weather Service
- 12 secrets of Mountain States Telephone & Telegraph Building
Got a place you want us to go inside and learn the secrets of? Email Debbie@TheDenverChannel.com.