Things To Do
Walk around/shop/eat/drink at Pearl Street Mall
This is the main drag/Boulder downtown area. Fun place to stroll around, lots of cute little stores. Get a coffee at Ozo. Drinks at Jungle. Rooftop drinks at Rosetta Hall. Beers/burgers at Mountain Sun. Bramble and Hair for a fancier dinner. Nepalese food at Sherpa's. Tacos at T/aco (eat outside on the patio.)
Picnic & Hike in Chatauqua Park
Best place to see the Flatirons up close/a really nice place to do a little hike and then picnic at the base. For hiking, recommend the Royal Arch Trail which is~3.4 miles round trip (pretty steady vertical up the entire way to the summit.) If you're looking for something shorter/easier, you can just loop around the Bluebell Mesa trail which is ~1.5.
Beers at Upslope Brewing Company
Our favorite brewery in Boulder
Hike Green Mountain
This hike is~4 miles. Not terribly vertical except for the last ~.75 mile to the summit. Close to Boulder and really nice peak views of the Rocky Mountains. You drive all the way up Flagstaff Mountain (where our wedding ceremony will be!) to get there. Be careful driving, always lots of bikers coming through!!
Hike Mount Sanitas
Two different routes (or both can be combined for a nice loop.) Either take the Lion's Lair route which goes through the woods and is a nice and gentle incline, or the East Ridge Trail which is short but very steep. ~6 miles total if you loop these trails. The parking can be pretty limited there especially on the weekend, but you are allowed to park in the neighborhood nearby which is very close to the trailhead.
Creek hangs at Eben G. Fine Park
If its nice and warm out-- highly recommend a creek day. We love to pack a couple of towels and a picnic and hang next to the water. Pro tip-- if you are packing any adult beverages, bring a koozie because the park cops are pretty intense about enforcing the rules around there since it's so close to the University!
Walk around Boulder Reservoir (or paddle board or Kayak)
Great place for a really easy stroll-- beautiful expansive views of the mountains (good anytime, but especially beautiful for sunrise/sunset.) If you park at Tom Watson Parking lot it's free, otherwise if you drive into the Reservoir itself via 51st street, there is a fee to enter-- but you can rent a kayak or paddle board there which is pretty fun. Stop at Avery Brewing on your drive back to Boulder!
Drive Peak To Peak Scenic Byway
If you've rented a car-- driving on Peak to Peak is absolutely stunning. Has incredible views of the Indian Peaks which sit behind Boulder. A good loop is to drive north from Boulder to Lyons, take St Vrain Drive (Route 7) up the canyon and then drive Peak to Peak south from there. Stop in Nederland for a coffee (Ned General Store) or pizza (Crosscut Pizza.) Then head back down to Boulder via Boulder Canyon Drive. Alternatively you drive down Sunshine Canyon or Lefthand Canyon and stop at Gold Hill, which is a own straight out of an old western film. Stop in the general store for a chocolate chip cookie.
Hike Dream Lake (Rocky Mountain National Park)
This is NOT in Boulder, hike is in Estes Park ~1 hour drive away.. but if there is one hike I would recommend to you in Colorado this would be it! Hike is located in Rocky Mountain National Park and luckily this early in May you (usually) don't need a reservation to enter, but make sure you check on the National Park website before you go. Dream Lake is ~2 miles round trip and not terribly steep. You can keep going to Emerald Lake for ~3 miles total.