Our favorite place to go for rooftop cocktails at sunset (they have plenty of heaters and gas fire pits), the rooftop with Flatiron views is gorgeous in October. Downstairs you'll find several international cuisines, desert bars, and American fusion stalls and a fun atmosphere with live music.
One of three of our favorite brunch spots. They don't take reservations on the weekend, but you can digitally join the waitlist before you get there: https://www.yelp.com/waitlist/snooze-an-a-m-eatery-boulder-2?utm_source=snooze-an-a-m-eatery-boulder-2&utm_medium=nw_restaurant_generic_flow
We highly recommend walking around Chautauqua park or hiking the first and second flatiron loop, a short but challenging hike. You'll be rewarded with incredible views of the Rockies on the backside and the Front Range on the other. We did our engagement pictures here! Stop by the historic Chautauqua Dining Hall afterwards for a beer and Colorado cuisine. https://www.alltrails.com/trail/us/colorado/first-and-second-flatiron-loop
If you're a fan of the Sleepytime Tea or any of the other iconic teas from this local company, we highly recommend taking a tour and sampling the goods of this awesome factory. They've been closed for the past few years and just recently reopened. $5/person and they don't take reservations. A highlight is the "mint tea room".
Rocky Mountain National Park, and it's surrounding town, Estes Park, are a must-see if you haven't yet. Go check out the Stanley Hotel for a historical ghost tour (where Stephen King's The Shining took place) and one of the world's largest whiskey collections. It's about an hour away from Boulder. To keep the park from overcrowding, there is a timed entry reservation system. It's not too difficult to get in if you plan in advance! See the remaining fall foliage colors and then go to Bird & Jim for a bison burger and truffle fries.