If you plan to stay closer to the city, then Red Rocks is a staple for many guests. There are many hikes around the park and the amphitheater can be explored during the day. Even just driving through the park and looking at the rock formations is a site to see.
If you have some time to kill whenever you are heading to or from the airport, I recommend stopping by Downtown Golden! There are so many shops to explore and restaurants and ice cream shops to eat in. There is also a free rock/crystal museum called the Mines Museum of Earth and Science that is cool for all ages. If you are looking for a place to grab a bite to eat or drink, we highly recommend stopping by The Golden Mill. They have a variety of vendors for anyone’s appetite and pour-your-own-taps of beer, ciders, wine, and mixed drinks! Just make sure to check in with the host stand before getting started.
If you are coming in early or staying late, we highly recommend exploring Denver’s Meow Wolf immersive experience. Walking through this interactive art installation takes about 3 - 5 hours, but it is worth a visit if you have the time.