Fly
Salamanca has no international airport, but they have a daily flights from Barcelona and Malaga with Lagun air and buses run frequently to Madrid with Auto-res 200 km away, and trains link the town with Madrid and Portugal with Renfe. Ryan Air flies to Valladolid from Brussels, Milan and London's Stansted airport, and Salamanca can be reached from there via a 1.5 hour bus ride.
Train
Take an afternoon Eurostar from London to Paris in just 2 hours 20 minutes, then the excellent Elipsos trainhotel from Paris to Madrid overnight, followed by a train to Salamanca. The trainhotel has cosy bedrooms, a restaurant and a café-bar.