From New York City

Direct: EWR → Bilbao
United

Through Madrid or Barcelona: JFK/EWR → Madrid or Barcelona → Bilbao Iberia, Air Europa, American Airlines, Delta

Trough Paris or Germany: JFK → Paris/CDG or Frankfurt → Bilbao
Air France or Lufthansa

TIP: Consider staying a night or two in Madrid or Barcelona if you’d like to extend your trip.