Piper and Nora share a joke at the very end of the book. On the roof of the prison where they're being held, they look out at the Congress Hotel and say "what a dump" (18.66). Ha.
The Congress Hotel is the exact same place where Nora packed the suitcase of money that landed Piper in prison, so these two have come full circle. Piper called the Congress Hotel a dump back in Chapter 1 (1.59), and nothing much has changed.
At the same time, they could also be talking about the Chicago prison we're they're being held. If it's the prison equivalent of the Congress Hotel, it makes Danbury look like the Four Seasons. Over a year into their sentences, they're both prison connoisseurs at this point, so we trust their assessment.