Around the Bozeman area, and about 10 miles or less. That's my limit!
1. Emerald Lake. In the Hyalite drainage. About 4 1/2 miles up to a lovely mountain lake. Graylings swim and jump.
2. Lava Lake. In the Gallatin Canyon. About 3 miles up to dramatic mountain lake.
3. Mount Blackmore. At the Hyalite Resevoir. About 4-5 miles up to a mountain top. Why? Because it's there. And because I can eat a MacKenzie River Pizza, a whole one, when I am done.
4. Bear Trap. Along the Madison River, just before you get to Norris. Everyone's favorite late fall/early spring walk. Watch out for rattle snakes and poison ivy. Don't go in the bushes.
5. The M. It's more a workout than a hike, because it is all of 10 minutes from downtown. 1.5 miles up to a beautiful view of the valley. Unless you take the 'most rigorous' way -- straight up the mountain.
6. South Cottonwood. My new favorite, south of town, west of the Hyalite drainage. Gradual assent, nicely shaded.
7. Middle Cottonwood. In the Bridgers, north of Sypes Canyon. You can hike up to the foothills trail or explore the ridge line.
Here are more suggestions.