Could you perhaps give a little bit more context? I looked up 'Winter Warmer' and I came up with a type of beer brewed in the fall/winter. I'm not sure what that would have to do with a two bedroom cottage though....
When I googled "Two Bedroom Cottage - Winter Warmer," I found a booking site for cottages in Australia.
I think they are marketing the cottage to people who live
outside Australia and experience cold winters in December, January and February.
If you rent the cottage during those months, you will experience the Australian summer.
The cottage is a "winter warmer" in the sense that it will warm you up during your cold (at home) winter.
That's how I understand it anyway.