Monday marked the official 125th anniversary of Minneapolis' City Hall building, which also serves as the Hennepin County Courthouse, a big milestone we wrote about a couple weeks ago.

Here are nine things we bet you didn't know about this iconic downtown building and clocktower.

1.The exact anniversary date is a little squishy.

Construction of the building actually started in 1887, but the cornerstone was laid on July 16, 1891. That cornerstone is located 30 feet above ground instead of at ground level because construction of the granite building had already started a few years beforehand. By the way, some of those individual granite blocks weigh 23 tons – that's 46,000 pounds – and were cut from quarries near Ortonville, Minn.

2.There are fossils in the marble walls.

If you walk in at the South 5th Street entrance, you'll notice some interesting shapes in the pink marble walls – those are fossils. We think that curly bit there is a nautilus shell.

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3.There's a plaque with what looks like a misspelling, but it's not.

The sign that says "Fovrth Street Entrance" isn't an old-school typo – that's just what the street was named back then, when v's often substituted u's.

4.Those green-tinted windows in the city council chamber aren't for fun.

When the windows were clear, council members appeared greenish on television, a problem with white-balance in the room, for you photography nerds. With the green windows behind them, it means councilmembers appear natural when proceedings are being broadcasted.

5.The bells in the tower used to be played by hand.

A man used to climb more than 400 steps to get to the tower to play the bells by candlelight. Now, members of the Tower Bell Foundation play the bells with the help of a keyboard in the first-floor rotunda.

6.The last execution in Hennepin County occurred in the 5th-floor attic.

A brick wall there, once part of the jail, is where John Moshik, who had been convicted of murder, was hanged in March 1898. There hasn't been another execution since.

7.41 faces are carved into marble columns.

They're known as "grotesques," and you'll find them in the marble columns on the ground floor near the elevators. Collect all 41!

8.The building has a green roof where a bee colony lives in managed hives.

We wonder if city hall staffers get a discount on honey …

9. Single women used to use tile to strike up romances.

On the third floor, a signature reading "Miss Lillian Cross" can be read on one of the tiles. At the time of the building's construction, some single women scratched their names on the top of a tile and addresses on the bottom in an effort to catch the attention of the men laying the tiles. There are approximately five million tiles in the building, and they were all installed by hand by workers of the American Encaustic Tiling Company. Call it the early Tinder.