In my well-traveled opinion, the Beartooth Mountains are the best kept "secret" in the contiguous United States. Ok, so maybe not a secret anymore, but it's so hard to get to, lodging is limited and access can also be tricky all compounding to make it a great area for getting away from folks into some rowdy terrain. Fun facts: the Beartooths contain all 26 peaks above 12,000 feet in the state including Granite Peak, the states highpoint and the iconic Glacier Peak which contains some of the greatest ski mountaineering lines around. Added bonus is they get great powder unlike much of Montana.
To get to Glacier Peak....from the town of Cooke City head out of town to the east on highway 212, you'll want a snowmobile for the long approach, or it's going to be a multi-day outing slogging through the flats for many miles. Get to Goose Lake and park the snowmobile here, this is where the wilderness boundary starts. Cross Goose Lake and hit the pass between Iceburg Peak and Sawtooth Mountain. This puts you into West Rosebud Creek drainage. You'll see the great western couloirs of Glacier Peak, head in that direction and down canyon past Glacier Peak. Tuck into the north side of the mountain to access "Catch a Fire", the "Patriarch" and the "Chounard" couloir. It's a healthy approach to ski Glacier in a day and it's more fun to make it into an overnight or two so you can tag multiple worthy lines.