Thursday

Boulder Tuesday Thursday Hikers: Join outdoor enthusiasts for a day hike with this leaderless, rule-following drop-in group that breaks into smaller groups and carpools to various trailheads. Drivers are reimbursed for expenses. Bring a lunch, water and snacks, and be prepared for all weather conditions; 9 a.m. Thursday, North Boulder Park, Seventh and Dellwood, Boulder; free; 303-494-8822.

Sunday

Old Man Winter Bike Rally and Run: Bundle up, and get read for an epic winter adventure. Riders can choose from a 50K course with rolling mixed terrain or a more adventurous 100K journey through Boulder County’s best gravel and canyons. Runners can choose a 5K or 10K course, both with great scenery and a mix of gravel paths and roads. There’s also a run/bike combo category; 10 a.m. Sunday, Bohn Park, 199 Second Ave., Lyons; $40-$100; 971-678-6291.