Extend routes into more rooms, chain several journeys, and maintain a labelled collection of many palaces.

Growth has three moves:

• Longer routes — continue the path through more of the building or down the street.
• More palaces — your home, your workplace, your commute, a childhood house; each is an independent store.
• A catalogued set — memory athletes keep dozens or hundreds of palaces, mentally labelled ("the school palace", "the digits palace") so they can grab a fresh, empty one on demand.

You built one to learn the skill; you scale by repeating the build, not by cramming.