Populate it

Who or what lives or dwells here? Who or what is visiting, exploring, or just passing through? You probably already know this, but make a list.

Don't limit yourself to people. Think about beasts, spirits, constructs, undead entities, and any other entity that the PCs might interact with.

If there are multiple denizens, then think about the relationships between groups and individuals. Factions and rivalries. Debts, alliances, and feuds. Familial ties. Love and hate and jealousy, all that stuff. Include some notes about these relations as you make your list.

If you expect the PCs to communicate with any denizens, then create them as NPCs, with tags, traits, an instinct, roleplaying notes, etc.