What is the importance of the cottage on the lough in the novel, TransAtlantic?

Ambrose's parents give Ambrose and Lottie a small cottage on the lough as a wedding gift. They spend hours there together, working on the cottage and building it into a retreat that they love. The cottage has a half-door and a sloping lawn. It is always subject to the weather. When Hannah lives there as an older woman, it's impossible to keep the entire house warm. There's a sunroom that was added years after the other rooms were complete. The cottage is near the water and is very private, though Hannah sometimes has to chase off interlopers. The cottage comes to represent family and security for Hannah. As she is preparing to leave it for good, she can still imagine Thomas walking into the rooms.