The tough 12.5-mile Barr Trail ascends Pikes Peak with a substantial 7400ft of elevation gain. Most hikers split the trip into two days, stopping to overnight at Barr Camp, the halfway point at 10,200ft. The trailhead is near the Pikes Peak Cog Railway depot; parking is $5.
If you're interested in doing the trail as a day hike, you can buy a one-way ticket ($22; first or last departure only) from the Cog Railway. You’ll be let out onto a spur trail 1.5 miles from Barr Camp where you can join the main trail to the summit (7.5 miles total).