The book opens with older Henry watching on as belongings of Japanese American families are carried out from the Panama Hotel. It's clear from the start that this hotel isn't just another building—it holds a great deal of significance for Henry:
The old Seattle landmark was a place he'd visited twice in his lifetime. First, when he was only twelve years old, way back in 1942— "the war years" he liked to call them. Even then the old bachelor hotel had stood as a gateway between Seattle's Chinatown and Nihonmachi, Japatown. Two outposts of an old-world conflict—where Chinese and Japanese immigrants rarely spoke to one another, while their American-born children often played kick the can in the streets together. The hotel had always been a perfect landmark. A perfect meeting place—where he'd once met the love of his life. (1.2)
The Panama Hotel represents all of Henry's memories and emotions from the past; when the basement is opened up, so are the floodgates to everything that he's tried to keep under wraps for the past few decades. It's the discovery of the Panama Hotel's basement that leads Henry to seek out Keiko Okabe—his first love—again. As the foundation of the building is explored, Henry begins to explore his own foundation, too, digging into his past to see what he can find.
The Panama Hotel is also where Henry and Ethel meet up after she reads his letter to Keiko. Upon his foundational romance with Keiko, then, Henry and Ethel build their lives, falling in love and eventually starting a family. We can think of the building as representing Henry in this way, then, with the visible parts—his long life with Ethel and Marty—standing on top of his past with Keiko.