It's warded so no one can winnow in. Upon entering, there is a main, wood-paneled room consisting of a kitchen to the right, a living area with a leather sofa covered in furs to the left, a small hall in the back that leads to two bedrooms and a shared bathing room, and nothing else. There's a hearth that is large enough to warm the whole place.
It responds to magic. Mor is able to unlock the door, start a fire, warm the water, and provide food with a wave of her hand. The house has been spelled to take care of anyone inside, they just need to wish or speak for things and it'll be done.
In the bathing room is a deep, sunken tub in the floor, large enough to accommodate Illyrian wings. The counters in the kitchen are made from wood and there is also a stove in the kitchen. There is a small dining table between the kitchen and living area. The bedrooms each contain a set of drawers, closets, and large beds. There is also a supply closet in the main area.
Feyre describes the cabin as not common, because everything had been made and appointed with care, but casual. As if this were the sole place where they might all come and not be anyone but themselves, a family.
Mor and Rhysand used to get sent to the cabin for "reflection" when they were younger. Rhys used to smuggle in books and booze for Mor.
Mor brings Feyre to the cabin when she discovers that Rhysand is her mate and that he kept that from her. She wants to be left alone to think over everything. Feyre discovers half a dozen cans of paint, paper, a few canvases, brushes, and other art supplies in the supply closet. She then spends the rest of the day and all through the night painting the cabin's interior. She is up and painting again before the sun the next day.
Feyre painted clusters of icicles drooping down the sides of the threshold. They melted into the first shoots of spring, then burst into full blooms of summer, before brightening and keeping into fall leaves. She painted a ring of flowers around the card table by the window, and leaves and crackling flames around the dining table. She also painted the Inner Circle. She painted the mantle of the heart to represent Illyrian wings. The window was framed with Mor's hair. Amren's eyes were painted above the threshold to the bedroom hallway. She adds Mor's eyes at her request. Mor then has Feyre paint Azriel's eyes next to hers and Cassian's next to Amren's. Mor paints some stick figures on the wall beside the storeroom door.
It's at the cabin that Feyre envisions the future she sees for herself. A direction, goal, and invitation to see what else immortality might offer her. Her future doesn't seem listless or empty anymore.
She spends the next five days painting every room.