The constant physical presence would rewire everything. Imagine a tidal force that breathes and thinks. A kingdom built in the shadow of a leviathan's nest isn't just coastal; it's symbiotic, or parasitic, depending on the century. Their architecture wouldn't be about defying the sea but appeasing it—curved, low-slung buildings from local stone, designed to withstand the dragon's movement tremors, not storms. Entire districts might be movable, on rafts or stilts, ready to shift if the nesting grounds shift.
Religion is the obvious one, but I think trade gets weirder. The most valuable export isn't pearls or fish, but 'drake-scale'—shed keratin polished into shields, or fertilizer made from guano-rich sand from the nesting beach. A forbidden, black-market trade in stolen eggs or molted whiskers could fund a whole criminal underworld. Their concept of law might be less about murder and more about 'scale-theft' or 'nest-desecration.' Even their calendar is shaped by the dragon's hibernation cycles or mating flights. You don't measure years by stars, but by the great sleep.
Forget chivalric knights; their heroes are the tide-speakers who can predict the dragon's mood from the brine pools, or the 'bone-singers' who craft instruments from washed-up rib fragments. Every lullaby, every epic poem, is about the deep's heartbeat under the cliffs. It's not a backdrop; it's a character, a landlord, and a god, all in one.