Hyalite Canyon (tons of hikes to waterfalls here), Storm Castle (good day hike right off of the Gallatin in the canyon), West Yellowstone ATV rentals, Cabin Creek Cabin (a rentable forestry service cabin deep in the backcountry), Fan Mountain, Boiling River (the only thermal feature in Yellowston you are actually allowed to get in) and so many more! Have fun and don't forget your bear spray!
@Bryce - I second Hyalite Canyon! While it's a bit of a drive if you're staying at the resort, it's worth it! It's a gorgeous area with some established camping (reserve your spots ahead of time if possible because it can book up fast!), a reservoir and really nice hiking. I highly recommend hiking Hyalite Peak trail. You can either turn around at the lake, or make the long hike up to the peak. Just get going super early before the thunderstorms roll in, and bring your bear spray!
If you like fly fishing, the Gallatin runs all along 191 and there is some nice, though somewhat technical, fishing in many areas and pull-offs. I'd highly recommend hiring a fly fishing guide to show you the good spots. If you want more of a floatable river, check out the gorgeous Yellowstone out of Livingston or the Madison out of Ennis. Again, it's a bit of a drive but absolutely worth it.
Have fun, and let us know what you get yourself into!
If your trip is to Big Sky, stay there. Beehive Basin is a beautiful hike in that area. On the north side is Spanish Peaks, a hike with waterfalls.
You can also mountain bike on the ski hill.
There are many hikes through the canyon on HWY 191 from Bozeman to Yellowstone.
The boiling river in Yellowstone is on the east side of the park. Kind of far to travel for a soak. Also, due to Covid, it may be closed.
The key is to get up early and get going so you can park at any of the trailheads.
If you are needing a campground, book early.
Hyalite is nice towards the end of June and later. It’s a good place to stay for a couple of days. It hits your request for lakes and waterfalls. It is a bit out of the way for a day trip.