If you've driven past Idaho Springs on your way through the mountains, then you've probably noticed the Argo Mill and Tunnel.

You can't miss it. The building is bright red with the letters A-R-G-O spanning across the top. But what is it?

ARGO Mill and Tunnel // Facebook
ARGO Mill and Tunnel // Facebook
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The mill is actually the No. 1 attraction in Idaho Springs — at least according to its website. Known as the Historic Argo Mill and Tunnel, the building is "one of the largest, most well-preserved historic gold mills in the world."

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Uncover Colorado reports that the attraction started with the Argo Tunnel, which was erected after the Colorado Gold Rush in 1893. The Argo Mill came soon after, and miners used it to process more than $100 million worth of gold ore.

ARGO Mill and Tunnel // Facebook
ARGO Mill and Tunnel // Facebook
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The Argo Mill and Tunnel continued to run through January of 1943, when a cataclysmic flood — coupled with the effects of World War II — forced its closure. The mill's website notes that it sat dormant until 1976 after a local decided to reopen it for the public to enjoy.

Today, the mill offers tours, gold panning trips (you're guaranteed to find treasure), and a gift shop.

ARGO Mill and Tunnel // Facebook
ARGO Mill and Tunnel // Facebook
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The gift shop is open from 10 a.m. to 6 p.m. (10 a.m. to 5 p.m. in the winter) seven days a week; however, tour schedules vary depending on weather and road conditions.

You can view specific tour schedules and book your trip here. Once you book your adventure, put your hiking clothes on and get ready to experience this iconic piece of Colorado history.

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