This is the standard route on Torreys Peak, and is recommended by Colorado Fourteeners Initiative as the peak's most environmentally-sound route.
Distance, Round-trip: 8.0 miles
Elevation Gain: 3,040 feet
The topo above, submitted by odysseus, shows another popular option, which is combining a hike of Torreys Peak with its neighbor, Grays Peak, the highest point on the Continental Divide.
Start at the Stevens Gulch Trailhead, which can be accessed from I-70 at the Bakerville exit (Exit 221). The drive up the dirt road can be a bumpy one, and I would recommend a 4-wheel drive or at least a high-clearance vehicle. In winter, this road is closed, so you can plan on adding an extra six miles to your trip. The road splits at the Grizzly Gulch Trailhead. Be sure to stay left as you continue uphill to get to the Stevens Gulch Trailhead. You will reach the trailhead after three miles. The hike begins at 11,230 feet, about at timberline in a very scenic valley. Follow a wooden foot-bridge across the creek, and begin your trek up Stevens Gulch.
The Grays Peak Trail is easy to follow upward through Stevens Gulch. In summer this is a crowded route, and it is best to start early to avoid crowds (and thunderstorms!). There is often a beautiful array of wildflowers, and do not be surprised to encounter some mountain goats along the way!
This trail ascends Grays Peak for quite some time, and eventually you come to a fork in the trail. Follow the trail to the right, toward the 13,700 foot saddle between Grays and Torreys Peaks. There is often a semi-steep snow slope here, as there was when I hiked this in July.
Follow the relentless switchbacks up Torreys Peak's south slopes all the way to the summit.
Water, camera, good hiking shoes.
In winter, snowshoes are a must, while crampons and ice ax may also help out on the steeper sections.