Jonas's cabin is where Bree, Daniel, and Jonas stayed during Snow Angels through Proving Bree Wrong. Its exact location is unknown, but it is secluded somewhere in the mountains. When they were en route to the cabin, Jonas called ahead to have the heat turned on, so there are apparently some sort of caretakers nearby.
Bree had found a Theta+Pi ligature at the cabin which she thought was related to the three-legged Theta+Mu ligature. She believed that Jonas was involved in the Order and tied him up. Jonas escaped, only to sneak back in to the crawlspace in the cabin to locate evidence to prove his innocence. In On The Road Again, it is revealed that Jonas's father had written a document called "The Order in the Modern Empire" that was anti-Order, aka The Resistance.