During the winter season, bears should go into caves on the first floor and sleep. They should still have an aggro radius and if you get too close they immediately engage you in rage mode.
Possibly make a bear dungeon, were its a new cave icon entrance anywhere there is a cliff and is labeled as the Bear Den, you can go deeper into the den by falling in holes meaning you cannot return unless you find a hill (acts the same way stairs do in cabins) to return you to the entrance or descend more into the dungeon.
You can also mine on those lower levels too but need the strength/skill, if you start mining you get bears to constantly spawn and attack, these bears produce no resource otherwise they could be farmed infinitely for resources. A benefit to mining in the dungeon is the quality of the stone you can get can be higher then normal on that respective floor or possiblity of getting lower level items in the Den. Make it so you have to build mine supports and the bears that spawn when mining in the dungeon actively try and destroy the supports (For disturbing their sleep). If a bear destroys the pillar everyone in the radius gets caved in on and knocked out (Bears are deadly so it would be risky). To make a cap on how much can be mined, just make it so no matter your stats/gear it would be too hard to mine after a few grid boxes in. Also be lucky if there is natural supports.
For the final boss/Den Mother, make them very difficult and very rewarding. Dropped resource can be made into a ridiculous curio, Bear claw weapon to be crafted from their claws (using unarmed as a primary stat), Den mother tooth which can be made into a better bear talisman necklace which increases strength and constitution based on quality drop and has a high chance to have an extra gilding if you put another den mother tooth or other bear teeth as the gilding with a max of 3-5 teeth or something.That could also be said for any of the bear equipment just make a better version with Den Mother items. Also would be cool to get the hide, dry it and then be able to place it on the floor as a rug, or actually use it for something useful instead of cool factor.
The entrance caves in when finished and everything in the dungeon is wiped like the other dungeons.