Colorado School of Mines Geology Museum in Golden (always free)
If you are spending a day in Golden and looking for free attractions, The Colorado School of Mines Geology Museum has a large display of rare gemstones, and their mining display downstairs should not be missed! One of the main attractions at the School of Mines Geology Museum is a moon rock collected during the Apollo 17 lunar mission!
When:
Monday - Saturday 9am - 4pm
Sunday 1pm - 4pm
Where:
1310 Maple St., Golden, CO 80401
The Museum is located in downtown Golden on the Colorado School of Mines campus, in the General Research Library building.
Check their web site for details: 
Keystone Ski Resort Free Scenic Chair Lift Rides
Keystone Ski Resort offers free summer scenic chair lift rides every Friday from 3-7pm, starting June 14 and continuing until summer activities close at the end of August. The views are incredible so I would definitely recommend taking a Friday to check out Keystone.
U.S. Mint at Denver Free Tours (Monday - Thursday)
Denver Mint Tours are closed for construction through February 27, 2014.
If you ever wanted to know where that change in your pocket comes from, the free Denver Mint Tours are the place to find out! Tours are free of charge Monday through Thursday at the United States Mint in downtown Denver. Reservations must be made in advance through the United States Mint Tour Reservation System
The Denver Mint building is highly secure, so you will need to pass through a security screening before your tour begins. Many common items are not permitted on the tour, such as purses, check their web site for a detailed list of prohibited items. The tour itself is very informative and interesting, discussing not only how new coins are made but also America's coin making history.
When:
Year-round, Monday - Thursday.
Reservations are required.
Be at the tour entrance 30 minutes prior to your tour time.
Location:
320 West Colfax Avenue
It's just off the southern end of the 16th Street Mall near Civic Center Park.
Visit their web site for tour details and reservations:
Smithsonian Free Museum Day
Every year some of the best museums in the USA take part in the Smithsonian Museum Day.
Denver Museum of Miniatures, Dolls, and Toys
For the dollhouse fan in every little girl at heart, the Denver Museum of Miniatures, Dolls, and Toys has a Community Day on the first Sunday of every month, from 1 pm to 4 pm.
Zengo (Downtown Denver)
The first thing that hits you when you enter Zengo near the 16th Street mall in downtown Denver is the atmosphere. The low lighting, the expansive bar and the couches in the lounge all say one thing- "I am hip and young in Denver."
University of Colorado Museum of Natural History at Boulder (always free)
The University of Colorado Museum of Natural History is a free natural history museum on the CU Boulder campus. They have excellent changing exhibits, a dinosaur section, and an extensive bird display. A small donation is requested to help keep the museum open and free. This is a fun small natural history museum for adults and curious kids.
When:
Monday - Friday 9am - 5pm
Saturday 9am - 4pm
Sunday 10am - 4pm
Where:
The Henderson Building on the CU-Boulder campus, between 15th and 16th streets east of Broadway.
For details check their web site: