Cairn

Inspiration

Street art has always had a problem; it's temporary, and nobody knows it exists until it's already gone. We wanted to build something that gives it an audience and a reason to go looking. No feed, no algorithm. If you want to find the art, you have to actually go there.

What it does

Cairn is a discovery app built around physical QR markers placed in the real world by artists. The map shows you roughly where art exists, never exactly. You go out, find the marker, scan it, and the artwork reveals itself. It's yours permanently. But each piece only lives 30 days, and you only get one chance to find it.

How we built it

React Native (Expo 56) · Supabase · Mapbox · TypeScript · Location is stored as a geohash only, never exact GPS. One-time discovery is enforced at the database level with a unique constraint. A Supabase edge function handles the 30-day expiry server-side so it can't be spoofed.

Challenges we ran into

Getting Mapbox running on Expo, building the expiry system so it couldn't be tampered with client-side, and designing the map to deliberately withhold information without frustrating users.

Accomplishments that we're proud of

The full tag lifecycle works end to end, submit, approve, countdown, expire, entirely server-driven. And the map actually makes you want to go outside.